Making a reloading manual.

[mrawesome22]

When "they" make reloading manuals, is there an industry "bullet distance from the rifling" standard?

In other words, if they found a max charge of 37.5gr varget with the bullet .030" off the lands for a OAL of 2.350", shouldn't I be able to use more powder with a bullet .030" off the rifling but at an OAL of 2.475"?

Since my OAL gives exactly 1/8" more case volume, but is the same distance from the rifling as theirs, pressure should go down in my load and I would have to use more powder to get the same pressure as the manual. Right?

I ask this because I have NEVER, so far, come across a book maximum load that gave me ANY signs of excessive pressure. But my OAL lengths are always quite a bit longer than book OAL.

Now I know everyone preaches the value of the book maximum. But if I have more case volume, shouldn't I be able to use more powder than them?

 

[rwilson452]

The values in the manual are for minimum length as published by SAMMI. doing that way the load should be safe in any gun constructed to SAMMI specs. If they used Max COAL and the user used Min COAL there could be a real problem. To Answer you question yes it's likely you could go a little over the listed max. BUT Be REAL CAREFUL. once your up in that range pressure builds very fast with very little increase of powder. The difference between shooting on a cool day and a hot day could be enough to ruin your day. It has been my observation that the most accurate load are less than max. now if your just want to see how much powder you can stuff in a case before failure. please let everyone around you know your looking a failure to happen so they can be elsewhere.

Making a reloading manual.
When "they" make reloading manuals, is there an industry "bullet distance from the rifling" standard?

In other words, if they found a max charge of 37.5gr varget with the bullet .030" off the lands for a OAL of 2.350", shouldn't I be able to use more powder with a bullet .030" off the rifling but at an OAL of 2.475"?

Since my OAL gives exactly 1/8" more case volume, but is the same distance from the rifling as theirs, pressure should go down in my load and I would have to use more powder to get the same pressure as the manual. Right?

I ask this because I have NEVER, so far, come across a book maximum load that gave me ANY signs of excessive pressure. But my OAL lengths are always quite a bit longer than book OAL.

Now I know everyone preaches the value of the book maximum. But if I have more case volume, shouldn't I be able to use more powder than them?

 

[mrawesome22]

Thanks for the input Wilson.

 

[Unclenick]

Actually, you'll find, especially with lighter, shorter bullets, that manuals often are well below SAAMI COL numbers. That also applies to bullet shapes that would touch the lands before the more common spitzer nose forms do. A round nose or wide meplat flat nose, for example. You often need to look at your bullet manufacturer's manual to get the recommended COL for one of their specific bullets.

You are correct that moving a bullet forward, provided it does not actually touch the lands, makes more room and will allow for more powder. Notice, however, that the pressure peak change is dependent on the % increase in powder volume created under the base of the bullet. Thus, moving a .45 ACP forward 1/8" of an inch is a much bigger percent powder volume change than moving the bullet forward 1/8" in a .25-06 would be, and therefore requires a much bigger % change in powder charge to come back up to the same chamber pressure as the more deeply seated bullet had.

CAUTION! THE INFORMATION BELOW IS FOR EDUCATIONAL PURPOSES, ONLY, AND IS NOT TO BE TRUSTED IN A REAL GUN TO BE TRUE. ALL LOAD INCREASES MUST BE WORKED UP TO VERY CAUTIOUSLY!

In very rough terms, for bottleneck rifle cartridges if you measure the water weight volume of a fireformed case from your chamber, subtract from it the amount of water weight the bullet displaces seated at the manual's COL, and then again, seated out at your longer COL, then take the square root of the quantity arrived at by dividing the larger volume by the smaller volume, you may then multiply the result times the maximum charge for the bullet seated at the shorter COL, and you will be in the ballpark of a matching pressure longer load, and can work up slowly towards that higher number.

For example, a .243 Winchester case with an 80 grain Speer SP bullet seated to 2.710" has a water volume under the bullet of about 51.5 grains. If you move the bullet out 1/8' to 2.835" COL, the water volume under the bullet grows to about 53 grains. 53/51.5=1.029. √1.029=1.014. So, multiply the old maximum charge by 1.014 to be in the ballpark of where your new charge would be. Sometimes the result will be a little high, and sometimes a little low, so work up watching for pressure signs. Generally speaking, the faster the power the more it overestimates, the slower the powder the more it underestimates, but it will be in the ballpark, either way.

Interestingly, in the short fat .45 ACP, despite the fast powder, it underestimates the increase needed by 30%. I think the formula is only precise enough for small changes in case volume, perhaps not exceeding 5% or so.

If you want a more accurate result, get a copy of QuickLOAD at neconos.com. Enter the maximum load from the manual, using the manual's COL and your fireformed case's water volume, and calculate the peak pressure. Change the COL to your new, longer COL and increase the powder until the same pressure results. The program is excellent for that kind of comparative load calculation.

 

[mrawesome22]

Hmm... very intersesting indeed Unclenick.

 

[Scorch]

Be careful, as you load closer to the lands, pressure increases because the bullet has less distance to build velocity to help it overcome the resitance when the bullet begins graving when it engages the rifling. So even though your case has a smidgeon more available capacity, you could actually have to reduce your powder charge.

 

[scsov509]

Be careful, as you load closer to the lands, pressure increases because the bullet has less distance to build velocity to help it overcome the resitance when the bullet begins graving when it engages the rifling. So even though your case has a smidgeon more available capacity, you could actually have to reduce your powder charge.

+1. That's why I always back off and work loads back up when I make any changes in a given load. Especially important when you're getting near max or looking for something near max.

 

[SL1]

The COAL values in the manuals don't help much in determining how to change a load when the bullet is seated to a different length. The pressures are measured in a test barrel with "standard" dimensions, which would seem to specify the bullet jump for a specific bullet (shape) at a specific COAL. But, throats wear in test barrels just as they do in our own rifles. It has been ALLEDGED that some of the hot loads in manuals come from the testers using eroded test barrels.

It would be nice if the manuals specified bullet jumps in their tests. That would at least allow handloaders to determine if their own rifles may create higher pressures.

I am not aware of a formula that can be used to calculate pressure differences from diffrences in bullet jump, ALL OTHER FACTORS BEING EQUAL.

I am also a little confused by Unclenick's post. If there was no change in bullet jump (that is, if the rifling was moved the same distance that the bullet was moved as the cartridge was made longer), then I think the pressures are about the same if the loading density is kept that same. That is, the powder charge could be increased in the same ratio as the powder space is increased. (That works for small changes, so long as the powder burn rate stays near optimum for the powder space and bullet sectional density of the cartridge. DO NOT try to use it compute Bullseye loads for your .25-'06 from data for the 25 ACP cartridge!)

I don't know why Unclenick used the square root of the powder space increase to calculate the increase in his charge weight. (I do know that, for the SAME POWDER SPACE, the pressure increases as the square of the powder charge, but that is not the same thing. For a fixed powder space, velocity tends to increase linearly with powder charge, and pressure must increase as the square of the velocity. So, pressure does increase as the square of the powder increase, but only for the same powder space.)

I don't know if Unclenick's formula is intended to take into account the effects of decreasing bullet jump, also. But, without knowing how much bullet jump decreases, I don't see how his formula can work. In rifles with a lot of "freebore", a COAL change of 0.05" might only change the bullet jump from 1" to 0.95" (5%) while the same COAL change in a custom target rifle might change it from 0.05" to 0.00" (100%).

SL1

 

[castnblast]

awesome22, recall the pm I sent you when we started experimenting w/ benchmark...I had worked up loads on some remi hp's on my 22-250, and had a bolt lock up .5 under max. Of course I wasn't loading for that specific bullet, but never in my 20 years of RL had that happen...I measure and remeasure all my charges, and trickle them down...then remeasure again - on my work ups...This was not an eroneous measure error.

 

[WESHOOT2]

assume NOTHING

The ONLY "always" in handloading I've found is "...but not always..."

 

[mrawesome22]

Yes castnblast I remember that. Anyway, I've been to book maximums with every powder I've tried so far and have never come across one sign of over pressure. The only remotely close sign of over pressure was some flattened primers that I later ruled out as flattened because of excessive headspace.

I'm getting the velocities I want and the accuracy I want but... color me curious. Maybe that 1/2" group would turn into a 1/4" group if I just went .2gr over what the book says.

Now I don't recommend it, and I advise against it, but I'm going to start experimenting with over book max's in my 700VLS.

I'm going to start with IMR4064 and Varget. Since my scale is accurate +/-1/10gr, I figure I'll start .2gr over book max and see what happens.

I will be using a chronograph and I am very well versed in the signs of over pressure. I just don't have any first hand experience. Yet.

I'll keep you all informed.

 

[Bullet94]

I tend to believe what William C. Davis, Jr. says here –

“It is obviously possible also to increase the free run simply by seating the bullet more deeply in the case. That has two effects on chamber pressure, which are in opposite directions. The increased free run tends to decrease pressure, but the decrease in powder space increases the loading density, which tends to increase pressure. Which effect will predominate depends on the characteristics of the particular load and gun. In most full-charge loads, it is found that the pressure decreases at first as the bullet is seated farther away from the lands, but beyond some particular seating depth, the pressure begins to rise again as the powder space is further reduced. In revolvers, the free run through the cylinder is always relatively great, and increased seating depth always increases the chamber pressures.”

My edited version of the above -

It is obviously possible also to decrease the free run simply by seating the bullet at a longer OAL. That has two effects on chamber pressure, which are in opposite directions. The decreased free run tends to increase pressure, but the increase in powder space decreases the loading density, which tends to decrease pressure. Which effect will predominate depends on the characteristics of the particular load and gun. In most full-charge loads, it is found that the pressure increases as the bullet is seated closer to the lands.

You might find this interesting regarding pressure and seating depth (taken from another forum) -

please quote your sources regarding the assertion that "guns (many??) have been blown up by seating into the lands." I don't believe this to be true. I don't believe that ANY guns EVER have been blown up by the simple act of seating into the lands...........................In fact I don't believe that you or anyone else can document so much as a velocity change from seating .001 into the lands VS .001 off the lands, or even .010 off the lands VS jammed, accurate documentation/testing will prove that the change is so small as to be theoretical, "lost in the noise" of ES..................(there can be no pressure change, jump, spike or blowup without a corresponding velocity change.) On this note, I'll further state that the neck opens up to seal the chamber against gas incursion BEFORE the bullet leaves the caseneck, it HAS to for the case to be properly perfoming its main function, that of acting as the seal or gasket which prevents gas from blowing out of the action. Engraving the bullet into the lands requires a force of approximately 600lb actual, the chamber pressure must reach 10,000lb to effect this.............the neck opens up to seal at somewhere around 4,000-6,000psi depending on thickness with many turned BR necks sealing at MUCH lower pressures, like under 1,000lb. ((((((If some of you are inclined to run the numbers, let me add that the 10,000lb figure applies to a wide range of calibers from .224 to .338, due to self compensation mechanism of neck diameter to case-size)))))

Point is...........NO AMOUNT of change of seat depth or of tension can alter the fact that the bullet is just setting there while the neck opens up to seal. (A possible exception is some of the new Win Shortmag stuff, hence some of the problems associated with them.)

To recap:

---6,000psi (max) the neck lets go entirely of the bullet.
---10,000psi the bullet starts to move.
---12,000psi the entire case is ironed to the casewalls clear back to the head.
---45,000psi to 70,000psi "Peak Chamber Pressure"........the bullet has moved about 3/8 of an inch.

Now, if you choose to back a bullet off of the lands by 30 thousandths you can expect a drop of about 1000psi from peak chamber pressure...........so conversely if your initial load were set at 30thou off and you THEN jammed into the lands you could expect a spike of around 1000lb, maybe 2%. This COULD theoretically wreck your brass but it's a LONG way from blowing up a rifle. In fact, even if you were on the raggedy edge of your gun's personal MAX you'd maybe leak a primer, that's it.

BTW..................when seating into the lands be suspect of any quotes exceeding .002-.005 with bullets other than VLD's. Typically light varminting bullets will go no further than .003 before being re-seated BY THE LANDS themselves.....typical Match bullets will stop engraving at .002. I'll jump out on a limb in guessing that the 90's may tolerate as much as .004 before they too are reset by the lands.

If the above is correct, seating depth (longer OAL’s) doesn’t effect pressure a lot (1000psi), but increasing powder will.

.

 

[SL1]

Bullet94,

Your second quote has a lot of interesting information, most of which I had not seen before. But, you put your finger on the problem of using it when you said "If it is true..."

Do you know what methods or sources the quoted individual used to write what you quoted? It would be helpful to me (and probably others) if I could get back to his sources and understand the basis for the numbers provided.

What you quoted seems plausible, especially since it only compared bullet jumps of about 0.01" to jamming the bullet by about 0.001".

My caution would be that there might be a lot more effect than a 1000 psi max pressure increase with a max load that was developed with the bullet something like 0.3" of the lands (not an uncommmon jump in a factory hunting rifle) if it is moved up to touch the lands. I won't go into the math of examples, here, but just note that the velocity changes (for the same amount of powder) between rifles (and Contender barrels) that do and do not have a lot of free-bore indicate that the pressure differences must be much greater than 1000 psi. A 1000 psi change in a 60,000 psi cartridge should give only a 0.008 (0.8%) increase in velocity, which would be a 24 fps difference in a 3000 fps cartridge. But, actual velocity differences can run in the hundreds of fps.

But, I think the point about using small increments and looking for pressure signs is essentially right. That should keep you safe enough so long as you are using a gun that can handle really high pressures without coming apart. That is really only a strong, bolt action rifle or a strong lever action with a front locking bolt. In others, the pressure signs that can be readily observed (action sticking, primer pocket expansion, even primer flattening) can occur at too high pressure to be safe in the guns that are designed for only 14,000 to 20,000 psi.

SL1

 

[Bullet94]

SL1 The quote was taken from here -

http://www.benchrest.com/forums/showthread.php?t=27109&highlight=bullet+seating+depth+question

I did my own test -

The test I did was trying to find out if loading into the lands created Dangerous pressures, as I have read this on the net before. I also read a post made by alinwa where he stated that he didn’t believe seating into the lands would create Dangerous pressures. I believe alinwa also stated if there was a pressure increase there would also be an increase in velocity. alinwa If I’m wrong about this please correct me. Anyway I had always believed seating into the lands might be dangerous, but after reading alinwa’s post I decided to try a test of my own. I don’t have anyway to measure pressure, but I do have a chronograph so here is a test I did.
I’m shooting 308 in a Shilen barrel 1/12 twist. I am shooting Burger Moly 185gr VLDs. I used Lapua brass that has been fire formed. The two cartridges were identical except one was seated into the lands and the other was seated off the lands.
The Jam length for my rifle measured 3.300. The cartridge that had the bullet seated into the lands measured 3.297. The cartridge that had the bullet seated off the lands measured 3.267. The distance to the start of the lands measured 3.277. All measurements were made using a Sinclair bullet comparator.
One cartridge had the bullet seated into the lands .020. I loaded 3 of these cartridges.
One cartridge had the bullet seated off the lands .010. I loaded 3 of these cartridges.
All were shot through my chronograph and velocities are listed in fps.
N550 powder 44.0gr was used for all loads.

Bullet seated into the lands .020 –
Average - 2488
High – 2500
Low – 2480
ES – 20.1
SD – 10.5
AD – 7.9
Bullet seated off the lands .010 –
Average - 2508
High – 2517
Low – 2501
ES – 15.7
SD – 8.0
AD – 5.8

More Velocity seated off the lands. I attributed this to the bullet being seated into the case more creating more pressure. I realize that this difference could just be the chronograph, but at least there wasn’t a big increase in velocity so I assume there wasn’t a big increase (Dangerous) in pressure when seating into the lands. The powder charge I used wasn’t a MAX pressure load just encase.

 

[mrawesome22]

Well I finally had some free time to do some testing today in my faithful 700VLS in 22-250Rem trim. I tested a 50gr VMAX with IMR4064 powder. I was trying to see just how high a charge I could get to before seeing signs of pressure.

Now the highest charge I could find in any book was a max load of 37gr. I have reached this load in my gun and it shows zero signs of too much pressure. With 37gr IMR4064, a 50gr VMAX, WLR primer, once fired Win cases, fireformed, necked sized with a Lee collet die, bullet ogive .030" off the rifling, I was getting about MOA groups. This was the best I could ever get this combination to shoot.

But as stated in my earlier posts, I wanted to see some signs of pressure. So I loaded 5 rounds at 37.5gr IMR4064. These shot a 3/4" group with zero signs of over pressure. Velocity raised about 50fps as expected. On to 38gr.

38gr IMR4064 showed no signs of over pressure, a 5/8" group and flew out at 3900fps. Now we're getting somewhere. So I decided to bump up to 38.5gr IMR4064.

Folks, we have a winner. 38.5gr gave me damn near a ragged hole with no signs of over pressure. So I loaded 5 more with the same brass and got a 10 shot ragged hole. I was gleaming. They were screaming out at 3980fps and finding their mark with extreme precision. No hard extraction, no flat primers, primer pockets still very tight, nothing set off any red flags. But since I was now 1.5gr over book max, my next loads went up in .3gr increments. So on to 38.8gr.

I have finally witnessed first hand signs of over pressure. The first round I fired at the 38.8gr charge dropped to 3900fps and bolt lift was more than usual. The 4 following it were exactly the same. But I was feeling fairly safe with my super duty safety glasses on and what not, so I bumped the charge up to 39gr. I found a max charge of 39gr on Steve's pages and was aiming to get there.

I loaded one round at 39gr, turned my head and squeezed the trigger. Good, still here and gun still in one piece. Bolt lift was WAY harder than normal. I had to stand up for leverage. Got the brass out and it had a nice big shiny spot on the head and the primer was flat as a pancake. Not pierced, and no black smudge, but flat none the less. Later I tried to seat a primer in this case and thought that a primer had not gone down into the tool. But one had, and the primer pocket was so loose that I couldn't even tell I was seating it.

And that concludes testing for today. I finally gained some first hand over pressure experience and found a great new load to boot. All in all it was a great experience.

 

[SL1]

Mrawsome22,

Using rules-of-thumb for powder charges and velocities and starting with the Hodgdon manual data, I would guestimate that you are reaching about 67,000 psi with your favorite 38.5 gr load. Both extrapolations come out close to that value. But, I don't know their test barrel length or yours. So, these extrapolations could be way off. If I start with data in some of the other manuals, I get less consistent results, some much higher. Maybe somebody with Quickload software can give you a better estimate if you provided them with the necessary inputs. (I will be buying that program later, but don't have it now to help you.)

I don't think your load will blow up a rifle that is OK when chambered with the new, short-fat 25 magnums. But, you will probably shorten your barrel's accuracy life if you shoot them a lot. It might be interesting to load up a bunch of those and set them aside as a "standard" that you can use in future years to see if they still give the same velocity and accuracy. Later tests with cartridges that are "set aside" now guarantees that any differences you see later are not due to changes in components or die settings over the intervening years. (Just make sure you shoot them at about the same temperatures.)

If you do that, let us know what you find each time you shoot some of those "standard" rounds.

SL1

 

[amamnn]

For what it's worth:

I've never witnessed a blown up rifle that anyone proved was destroyed by overpressure caused by seating in the lands. I just read an interesting account of how spec ops teams sabotaged ammo in enemy dumps during the Viet Nam adventure. It seems like they had to go to extreme lengths to get even cheaply made Chinese AK-47s to blow up reliably. I can't imagine a US made factory rifle exploding that way. Current Issue of American Rifleman.

Still, that is catastrophic damage and there are subtler ways of damaging your rifle at least to the point of inaccuracy. While it is true that seating closer to the lands increases START pressure, that does not mean that velocity is necessarily going to increase much if at all. There is a lot going on inside the gun during ignition. Powders burn differently under increasing pressures. Hotter loads = faster throat erosion = inaccuracy. Custom BR rifles are built to handle increased pressures but still some BR shooters consider a barrel to be gone after as few as 500 rounds. One person once told me he moved barrels off his match gun after 300 rounds and relegated them to fireforming 6mmppc brass. I offered to buy every other barrel from him for $100.00 and he never got back to me on that.

Jam seating is a technique useful in SOME BR rifles for various reasons affecting accuracy, not velocity. As someone noted, the hottest round is seldom the most accurate round and in BR shooting it is all about accuracy, not terminal performance. Custom BR guns generally feature very tight chambers while factory guns are larger, lately it seems the factory guns are being made with much longer leade making jam seating impractical if not impossible. Jamming the bullet into the lands as noted above only reseats the bullet deeper if you actually can reach the lands; if not you may not have sufficient neck tension/bearing surface. Jam seating is not used so much to increase start pressure as it is to uniform it.

Unless you have control over the neck tension of your loads (bushing dies and neck reamers are good for changing it or experimenting) your bullet will not seal the grooves. Sealing the grooves at the lands can help accuracy by eliminating most of the blowby gasses that precede the bullet down the barrel and out into the world. This can be especially helpful when using boattailed bullets which tend to let "leak" more gas than a flat based bullet.

A cartridge seated jammed in the lands and properly sized will contact the rifle at two points only during the initial ignition stage: the base and the ogive of the bullet. In a rifle that has been "blueprinted" using a cartridge that is properly aligned, this should result in a reduction or at least a uniforming of vibrations.

I have one BR gun (.308) that likes jam seated rounds and one (6mm)that does not. One should also consider that BR loads are quite often made without much consideration of pressure or neck tensions; the chambers are so tight, bolts and receivers so beefy as to support loads we would never consider in a factory gun.

For a more detailed discussion of this technique try the archives at benchrest.com or 6mmbr.com; you might find a lot of results looking for posts by Jackie Schmidt, who had been a proponent of jam seating.

 

[Unclenick]

Let's be careful out there.

Bullet94,

I am packing for a trip, or I would spend a bit more time here. I am stopping to put something in because a few potentially dangerous bits of misinformation were given above. First, the quote from the guy who thought touching the lands would make no difference because he didn’t see why it should, is an excellent example of uninformed speculation. He didn’t have all the facts, therefore they didn’t count. The difference between touching the lands and not touching them has to do with what physicists call static (stationary) and kinetic (or sliding) friction. When two materials come into contact, if you let them rest in contact for any period of time (fractions of a second are plenty), friction between them increases. For sliding a copper block sitting on a steel plate, the friction against sliding equals about 36% of the weight of the copper block. If you let the copper block stop for a moment, the static (standing still) friction you have to overcome to start it moving again is about 53% of the weight of the block; 17% greater than the kinetic friction.

For a bullet on the lands, this increase in friction that must be overcome to start it moving onto the lands causes a hesitation that gives the powder more time to burn and increase pressure. That is called the start pressure, so the static friction level increases it. The peak pressure, even though it isn’t usually reached until the bullet is moving in the rifling, will likewise increase because the powder got going faster, In the measured pressure example below, linked from RSI’s web site, the increase in pressure due to touching the lands (upper three shot pressure curves) was about 25%, compared with bullets seated 0.030" off the lands (lower three pressure curves). That increase is enough move a SAAMI maximum load up into proof load pressure territory. If the load was well above SAAMI maximum, however, as some hot handloaders make them, that 25% jump could be pretty hard on the gun. I would not expect an outright bursting of the gun, but you can bet steel strain and rate of fatigue will have been significantly increased. It will not be a healthy steady diet for the gun if it is to last, not even at standard proof load pressures.

Scorch,

The square root rule is a curve fit I did to pressure calculations in QuickLOAD. It is to keep pressure constant. The actual cause of pressure being disproportionate when you increase powder and volume equally has to do with increasing rate of burn and pressure. The exact mathematical model is a rather complex, but consider that increasing the case volume and powder charge does not change the size of the hole the gas all has to escape through, nor the bullet mass or start pressure it has to push through. That’s where the proportioning falls apart.

For example, you can pretty much stuff a .308 case with IMR 4895 under the 168 grain SMK at normal COL. That's about 44 grains for a standard volume case and and the pressure is just under 55 KPSI. Stretch that case out to .30-06 and fill the extra volume to the top with the same powder, about 56 grains under the same bullet, and you suddenly have over 70 KPSI.

 

[Bullet94]

Unclenick
I am interested in this so I asked the person that my quote was taken from to respond. Below is the response -


Alinwa quote -

Quote:
In fact I don't believe that you or anyone else can document so much as a velocity change from seating .001 into the lands VS .001 off the lands, or even .010 off the lands VS jammed, accurate documentation/testing will prove that the change is so small as to be theoretical, "lost in the noise" of ES..................(there can be no pressure change, jump, spike or blowup without a corresponding velocity change.)

Quote:
Now, if you choose to back a bullet off of the lands by 30 thousandths you can expect a drop of about 1000psi from peak chamber pressure...........so conversely if your initial load were set at 30thou off and you THEN jammed into the lands you could expect a spike of around 1000lb, maybe 2%. This COULD theoretically wreck your brass but it's a LONG way from blowing up a rifle. In fact, even if you were on the raggedy edge of your gun's personal MAX you'd maybe leak a primer, that's it.

Quote:
If I'm wrong on any of these issues please quote sources to lead me to truth.

Below is a response to your statements copied from another forum -

Quote from Unclenick:
First, the quote from the guy who thought touching the lands would make no difference because he didn’t see why it should, is an excellent example of uninformed speculation. He didn’t have all the facts, therefore they didn’t count. The difference between touching the lands and not touching them has to do with what physicists call static (stationary) and kinetic (or sliding) friction. When two materials come into contact, if you let them rest in contact for any period of time (fractions of a second are plenty), friction between them increases. For sliding a copper block sitting on a steel plate, the friction against sliding equals about 36% of the weight of the copper block. If you let the copper block stop for a moment, the static (standing still) friction you have to overcome to start it moving again is about 53% of the weight of the block; 17% greater than the kinetic friction.

For a bullet on the lands, this increase in friction that must be overcome to start it moving onto the lands causes a hesitation that gives the powder more time to burn and increase pressure. That is called the start pressure, so the static friction level increases it. The peak pressure, even though it isn’t usually reached until the bullet is moving in the rifling, will likewise increase because the powder got going faster, In the measured pressure example below, linked from RSI’s web site, the increase in pressure due to touching the lands (upper three shot pressure curves) was about 25%, compared with bullets seated 0.030" off the lands (lower three pressure curves). That increase is enough move a SAAMI maximum load up into proof load pressure territory. If the load was well above SAAMI maximum, however, as some hot handloaders make them, that 25% jump could be pretty hard on the gun. I would not expect an outright bursting of the gun, but you can bet steel strain and rate of fatigue will have been significantly increased. It will not be a healthy steady diet for the gun if it is to last, not even at standard proof load pressures.

http://www.shootingsoftware.com/pressure.htm

Alinwa
What do you think?


______________________________________________________________
Alinwa’s response -

Bullet94,


IMO the guy from the other forum is uninformed, he's applying incomplete data, basing his contention on a false premise. Surface-to-surface friction, static or kinetic is only part of the issue. His contention is not a new one, I've seen endless discussion, even articles with folks dragging weighted blocks of material around on table tops...... Incidentally I believe he's underestimating the effect. The measured difference between static or "breaking force" and sliding friction is more like 50% for copper on steel. AT THE PRESSURE PRESENT IN THE BORE......his "25%" figure comes from table top experiments using low surface pressure figures. I've seen these tabletop goofballs dragging around stuff like SHEETS of copper and thin blocks.

However, surface friction isn't the whole issue. Even if you somehow were to lubricate the interface to produce ZERO surface friction you'd have tremendous engraving force. To get the bullet into the lands something's got to give. That something is the bullet. The bullet must be redistributed, this redistribution comes at a price.


Without going into endless detail, suffice it to say that theoretical data agree with directly MEASURED data in this instance. The real difference between thirty thou out and touching the lands is around 1000psi. The maximum difference that one could realize would not exceed 1500lb. In the real world this gap is typically smaller because even a bullet set up to touch the lands gets a free run of up to .070 depending on the match of the ogive to the leade angle.


IF you had a blunt 7D or so secant ogive and IF you had a leade which was perfectly matched to it.............you MIGHT get the full 1000psi value for 30 thousandths. This is a far cry from 25%. 65,000-85,000psi plus 1000psi is more like a 1.5-2% increase. For the latest craze, 10D+ ogives, VLD bullet profiles, the change is lessened because the VLD profiles oooze into the lands incrementally. It's nearly impossible to get them butted to really jam. Lots of these guys who've traditionally "jumped their VLD's 20-30thou" don't realize that they're effectually running .100thou+ or using nearly an eighth inch of free-run!

((( To illustrate...... the difference between "just touching" and "deeply jammed" is between .065 and .075 on three of my 6BR barrels which are reamed with a 1.5degree half-angle........ from the point where the bullet is first marked by the riflings until a "deep jam" which slides the bullet back in the neck is 65-75 thousandths......this "deep jam" is nowhere NEAR the force required to engrave a bullet! Maybe 20lb VS the 500lb required to engrave the bullet.......)))


IMO the guy who's giving you advice on the other forum needs to hone his critical thinking skills I'm not sure how to rate the nice folks at RSI but they sure make a lot of contentions that aren't supported by other sources. The pressure trace data which purports to show the 25% increase is supposedly from a "good PPC load" at 35,000 to 41,000 psi.

!!!!!

45,000psi is down in 30-30Win M94 territory!

6PPC's run from 65.000 to 85,000psi.


I've had calls and letters from quite a few folks who own RSI systems. They're constantly confronted with "pressure trace" readings which show HUGE increases in pressure while reading only modest increases in velocity. A difference of 25% from one shot to the next isn't "modest"!! A 25% increase in pressure is hellacious..........and should result in a velocity increase to match the pressure spike.


A 25% increase in chamber pressure is certainly not to be discounted or treated lightly IMO........ running my 6PPC up to over 100,000lb over a 30thou screwup would make me uncomfortable! I believe that there's a fundamental flaw in the pressure trace data. In fact, if the RSI pressure trace data is to be taken at face value, if something as minor as 30thou seating depth COULD run you up TWENTY FIVE PERCENT!!! I can't see how the reloading companies could stay in business!

RSI seems to make decent equipment and talks a great line. I can't fault anything about them EXCEPT that I believe that their calibration is 'wayyy off and their interpretation of data is flawed. I ask you all, ANYone ANYwhere (except RSI ) to provide a chart where a 25% pressure spike is not accompanied by at least a 20% increase in velocity. Pressure/velocity are essentially linear EXCEPT at RSI...????

Here's something y'all ALL need to go out and TRY Go and test this stuff. I have many times.

IF RSI IS RIGHT.............then you can all go out there and prove it by working up a nice load IN THE LANDS and then backing it off .030 and watch as the velocity drops hugely...........(don't do the experiment the other way please!)


Now what's REALLY gonna' happen is that you'll back off thirty thou and barely be able to see it on your chronograph. I've accumulated months and months of data over the chronograph.


IN REALITY you will rarely see anything meaningful between 30thou out and touching the lands. Especially with other than supremely accurate BR equipment. I've done this seating depth stuff a bunch............and so have y'all out there in Shooter-Land ........can ANYBODY relate to a 25% increase from just touching the lands? 50-100fps velocity change is more the norm.......far from "dangerous" and FAR from "25%". It seems that the data presented by the RSI pressure traces increases this effect by a factor of 10!

In fact, the several books which I've got which detail the TOTAL effect of actual bore friction on the pressure curve all agree that the difference between normal frictive force and theoretical ZERO friction between the bullet and the bore falls somewhere under 2%. In other words fitting a bullet to the bore and lubricating it for zero friction VS stuffing a conventional bullet into the bore has very little effect. Robert Rinker in "Understanding Firearms Ballistics" states that TOTAL frictive loss including such effects as gas friction and heat loss account for only 2-4% of the total equation.


Harold Vaughn in "Rifle Accuracy Facts" actually built devices and measured the various effects of engraving force, friction and the amount of pressure needed to respectively engrave the bullet, expand the brass cartridge case for a seal and push the bullet down the bore.

MY question is this, If total hysterisis in a system only accounts for 4% loss, how can manipulation of this 4% yield a 25% change?


I'm open to suggestion, speculation or interpretation of the RSI data traces but I cannot agree that the 25% increases of "pressure" on the strain gauge readouts equates to actual pressure increases of the full 25%.


My speculation is that the RSI data reads only the top 10% of the curve. My contention is that the actual pressure generated in the "good 6PPC load" is more like 70,000psi and the strain gauge is reading only changes in the top 10% or differences of 5,000psi plus or minus around the mean of 70,000lb.


I further believe that the model of the bullet simply setting there "jammed" against the riflings until you "break it loose" is flawed. I don't believe that breakaway friction even enters into the equation. That the act of swaging the bullet into it's new shape, rearranging and redistributing the brass jacket and lead core is what change initial pressure curve. AND furtherfurthermore, the initial pressure spike is generated NOT by either friction OR swaging (another form of friction) but by Newtons laws of motion. That a fitted and friction-free projectile would exhibit a pressure curve that's within just a few percentage points of the real-world projectile.


I feel that while the 25% difference in the pressure curve is "real" it's not representative of total pressure.

I'm happy to be shown differently, I'd much rather learn something than be "right" 


thanks


al
_____________________________________________________


I kinda feel like a middle man here and this is not what this thread is about so, Unclenick
if you would like to respond to this here or at -

http://www.benchrest.com/forums/showthread.php?t=27109&page=3

Please do. I’m interested in this topic and believe others like myself could learn from this discussion.

 

[SL1]

I am reading all of this with some interest. Here are a couple of comments to consider:

1. I agree that engraving force probably will exceed the static friction vs sliding friction effect. But, remember that the friction force is a function of the force perpendicular to the surfaces, which needs to include the pressure forces that upset the bullet base and expand it against the bore surface. You can't measure that by mechanically pushing a bullet into the rifling and measuring the force required. That is just the engraving force and SOME of the friction force. And, if the pressure makes the bullet base increase in diameter in the throat before it reaches the rifling, that will increase the engraving force, too. So, I don't see how the actual "start" force can be measured realistically, unless the BULLET is equiped with a pressure sensor and an accelerometer and telemetry equipment (like some Canadian cannon experiments of long ago.)

2. Unclenick's pressure trace has TIME for the X-axis, but the work done on the bullet is proportional to the product of the pressure times the DISTANCE that the bullet moves under that pressure. So, you can't integrate the area under Unclenick's curves and see the difference in work UNLESS YOU FIRST TRANSFORM THE X AXIS INTO DISTANCE TRAVELED BY THE BULLET. That is hard to do properly, because the bullet is accelerating with time, and not uniformly.

3. Bullet velocity is proportional to the square root of the work done by the powder gases. So, for the same shape pressure curves with the X-axis transformed to distance instead of miliseconds, a 25% difference in area would only be expected to give a 11.8% difference in velocity.

4. The distance the bullet moves before the pressure peak is less than the distance the bullet moves after the peak, because the bullet is gaining speed over time in the barrel. So, the peak pressure is probably not as important to velocity as the decreasing part of the curve after the peak, because that is what is working on the bullet over a longer distance of bullet travel.

5. Putting that all together, I would expect a lot less than 25% velocity increase for a 25% pressure increase. Only something like 12% if the pressure increase occurs proportionately over the entire distance the bullet travels down the barrel, as one would expect from adding more powder. But, much less than 12% if the pressure increase affected only the peak and a little bit of the cureve around the peak. That second situation is more like what Unclenick's traces show.

If Unclenick chronographed the shots that produced those traces, we could answer the question about how much velocity change occurred with the pressure effects shown. How about it Unclenick, do you have the corresponding velocities?

SL1