Pressure increase when bullet is into lands?

[jepp2]

Is there a rule of thumb guideline for the approximate increase in pressure when you seat the bullet long and it is jammed into the lands of your rifle?

I seem to recall the estimated increase is around 7K PSI. My reason for asking is I am going to fire forming some 22-250 AI brass, and I intend to load the bullets so I have about 0.010" interference with lands so the case head is tight against the bolt face.

I do realize some of the pressure increase will be lowered due to the case expansion that occurs as it reforms from 22-250 to the Ackley Improved version of the 22-250.

 

[wncchester]

"Is there a rule of thumb guideline for the approximate increase in pressure when you seat the bullet long and it is jammed into the lands of your rifle?"

No. Someone may suggest one but it would be a lie because there're too many variables.

 

[SL1]

Jamming the bullet into the lands will certainly raise pressure some.

But, if the idea is to minimize case stretch by keeping the case head against the breach face when the cartridge fires, have you considered what will happen when the firing pin strikes the primer? IF it drives the case forward by seating the bullet farther into the case, then you will not be achieving what you are intending.

You could test that by making a dummy cartridge with a spent primer and the bullet seated-out as you intend to load the fire-forming cartridges. Put some magic marker on the bullet around where the case mouth will be so that you can see where the case mouth went with the firing pin strike. Then, chamber the dummy and pull the trigger. When you open the bolt, the bullet will probably stick in the lands and need to be knocked-out from the muzzle end with a rod. Be careful to do that in a way that will not change the shape of the bullet where you measure the COL. That is, if you measure from the tip, use a rod that does not contact the tip. Or, if you measure from the ogive, then use a rod that does not contact the ogive. When the bullet is out, reseat it to just the point where the case mouth has not scraped the magic marker marks, then remeasure COL. If it is what you started with, then the firing pin did not drive the case forward. Otherwise, you can see how much it drove it forward.

Another way to hold the case head against the breach face is to expand the neck to the next caliber diameter and then resize the neck only enough to get the case to chamber against the "false shoulder".

SL1

 

[wpsdlrg]

Wncchester is spot on - too many variables in order to calculate this.

Further, the technique of seating out enough to jam the bullet into the rifling (upon chambering) is ONLY intended for CAST bullet loads - and relatively soft loads at that. It has NEVER been considered safe for jacketed loads under ANY circumstances. It's use is generally confined to firearms with long, loose throats, such as some milsurp rifles (like Mausers), where it can serve to improve accuracy. However, as I said, it should NEVER be used with anything but relatively light, cast bullet loads !

If used, the general idea is to seat the bullet so that it just kisses the rifling when chambered, so to support the bullet nose and prevent any yawing (in the loose throat area). If shooting the loads in question in a firearm with a "normal" leade or throat, then there is NO need for this technique, anyway.

 

[mehavey]

Well, I'll have to disagree that its never safe under any conditions.

If -- say -- 0.010-0.015" into the lands -- was worked up as part of the load ladder established
for nominal pressures, it's a safe load.

The problem lies in being so close to the lands that you are on-again/off-again because of
mechanical tolerances... that's when pressures (and precision) go up and down.

Ditto when the bullet is so far into the lands that it gets pushed back into the case --
THAT's when pressures can get real interesting.

 

[wpsdlrg]

mehavey,

Technically, you are right - in a way. Certainly, if one downloaded enough to allow for the pressure spike associated with seating a bullet into the lands, then one could create a "safe" load. However, since we've already covered the concept that there are too many variables extant in order to calculate the actual pressure spike produced by such a practice - how would one calculate how much to download ?

Can't be done - not in a practical sense, anyway. So, it becomes simply guesswork.

It is well known that a pressure spike DOES occur, when a bullet does not have room to "jump" a small gap to the lands (when a bullet is seated into the lands)....and none of us can know how great the pressure spike will be for a given load.... therefore, there is no practical way to calculate a reduced charge, in order to make this practice safe.

So, unless one fancies taking extreme risks while reloading/ shooting....we are back to the understanding that it is a very dangerous practice. A technique best AVOIDED by any and all with any common sense.

Put another way : Just because it might be technically possible to jump off a bridge and survive.....does that mean that one SHOULD try it ? I would tend to say NO. Your answer might be different....but I hope not for your sake.

 

[mehavey]

That's why one works up the load from scratch -- so the pressures extant are the ones developed as part of the process. If/when the "standard" pressure signs appear (e.g., beginnings of a bright spot in the ejector cut-out), you're at ~70,000 and should back down a grain for everyday max.

The normal re-loader cannot rely on Manual/Book data for pressures in the best of circumstances -- as you note there are too many variables and this is why manuals vary all over the place.

Many manuals, QuickLoad, my Oehler, and casehead conditions are what I rely on to set my own parameters -- and usually best accuracy is obtained well below max.

 

[boondocker385]

Without the ability to measure pressure you and everyone else are just guessing. And guessing is a recipe for disaster.

 

[jepp2]

Without the ability to measure pressure you and everyone else are just guessing. And guessing is a recipe for disaster.

But that is exactly what you are doing every time you start with load you select after referencing several manual (which the starting load in one manual may be above the max load in another manual), and work up until you find the max load for YOUR components in YOUR rifle.

I want to thank everyone for sharing their input. I found the 7K reference I was remembering. It is listed in the additional information in the bullet starting pressure in QuickLoad. I also found the added case capacity as the standard 22-250 case is blown out to the 22-250 AI is around 7K. So "roughly" the added pressure of seating the bullet into the lands is reduced by the additional case capacity. So I am good to go with my fire forming.

 

[boondocker385]

With all due respect Jepp that isn't true unless all the manual makers are lying on their testing. Its when you go beyond what has been tested that you run risks without pressure testing equipment.

 

[jepp2]

Its when you go beyond what has been tested that you run risks without pressure testing equipment.

If you think that every listed load is safe in your firearm with the components you have on hand, then I think you will change your opinion in the very near future.

I don't have pressure testing equipment, but I feel very comfortable evaluating signs of higher pressure in my firearms as I work up loads. I do always refer to manuals as I develop new loads. I also evaluate the many signs of increasing pressure, not looking only 1 or 2.

Seating bullets into the lands is a fairly common practice among some groups. But just like when you change powder lots, when you make a more significant change, start low and work your way up. I was just hoping to find someone that had knowledge of the 7K PSI pressure estimation I was recalling. But then I found the source. Maybe it is 5K and maybe it is 10K, either way I am way below the SAAMI pressure max for my rifle. I have been loading for 45 years and have fired hundred of thousands of rounds without incident. I certainly wish to maintain that same record going forward.

 

[F. Guffey]

Sounds cool, “I seat my bullets .002” off the lands” I don’t, I want bullet jump, I want my bullets to hit the lands ‘a running’ I do not want my bullets taking off from a dead stop while stopped against the lands.

Those suggest that seating the bullet against is a “you bet, no problem, right away" answer take themselves too seriously, then there are those that believe it can not be done because of variables need to learn how to control variables.

Fire forming, I have used loads when fire forming that were at the jagged edge of over maximum load after the case was formed, time is a factor, another cute procedure when fire forming ‘seating the bullet long’.

Best advise when giving advise about fire forming, first determine the action, push feed, control feed??? No one should be giving advise about fire forming without knowing what action is being used.

Under all circumstances I determine the length of the chamber from the shoulder to the bolt face, after determining the length of the chamber I adjust my dies to control the length of the case from the shoulder to the head of the case, variables?

The Ackley Improved chamber has ‘head space built into the design. The neck on the standard case is short(er), the Ackley Improved neck is long(er), meaning? When the standard case is chambered the neck of the case is sized when chambered, and that beats seating the bullet long or ‘do as I do’, I neck up then form a shoulder on the case that eliminates “ALL THAT CASE TRAVEL”,

Managing variables, makes ‘can do’ reloaders.

F. Guffey

 

[F. Guffey]

“I am going to fire forming some 22-250 AI brass, and I intend to load the bullets so I have about 0.010" interference with lands so the case head is tight against the bolt face”

Jeep2. forgive, you can seat the bullet to the lands, not necessary, again, part of the shoulder will become part of the neck when you chamber the round, the rest of the shoulder and case body will be formed when the round is fired.

Only a serious reloader/fire former will scribe the case body/shoulder juncture and the shoulder/neck juncture before firing, those that have scribed the position of the 2 junctures notice the new case body/shoulder juncture is formed ahead of the old juncture and the new shoulder/neck juncture is ahead of the old juncture, for first time formers it must be explained to them the case die not stretch between the case body and case head, and the case will shorten when the case body and shoulder form, again, not between the case head and and shoulder but in total length.

F. Guffey

 

[SL1]

Guffy,

I agree with what you say about where the cases stretch, WHEN FIREFORMING IS DONE WITH APPROPRIATE STRENGTH LOADS.

However, if excessively high pressures are used to fireform, I have found that the case length does not decrease, and brass is drawn from the case body and shoulder areas to allow the case to blow-out to the "improved" shape. I think that is because the high pressure is sufficient to hold the brass neck tight against the chamber wall so that it does not slip back when the shoulder and body blow-out. (I don't lube cases when I fireform.)

I mention this because the OP discussed jamming bullets that are apparently jacketed into the lands for fireforming. I suspect that might produce pressures high enough that the necks won't slip back and shorten the cases. Perhaps the OP might think that is a good idea, but I don't. I would much rather have my cases get shorter than thinner.

SL1

 

[F. Guffey]

“However, if excessively high pressures are used to fireform, I have found that the case length does not decrease, and brass is drawn from the case body and shoulder areas to allow the case to blow-out to the "improved" shape. I think that is because the high pressure is sufficient to hold the brass neck tight against the chamber wall so that it does not slip back when the shoulder and body blow-out. (I don't lube cases when I fireform.)”

As he said he knew the pressure would be lower because the case must fill the chamber at the case body and shoulder, then ‘time’ become the factor, and then there is the .7854 thing. If events develop as you describe the neck will separate at the shoulder/neck juncture if the .7854 factor is equal even if the neck has less area to apply the .7854 thing.

Years ago I was told I was dealing with some scary methods and techniques, a smith took the time to send drawings with cautions, then he hit the send key, he was rare, he realized there was no way pressure could build to any level of danger because of the amount of space the case had to fill, the cases I was forming were ejected with necks that were .217” long before firing the neck was .385”, meaning the new shoulder when formed was .168” ahead of the old shoulder.

Because the older than me smith did not approach me in a manner rude I called Hodgdon and explained to them what I was doing, then they made cautions about load development, we agreed, my fire forming load could be at the edge of maximum after forming.

Then he added, there were a number of things he had never noticed before until he got a chance to put all the drawings side by side. I was not forming Ackley Improved cases to make a point he included them.

Part of the neck becomes part of the shoulder, part of the shoulder becomes part of the case body, and that just locks up bench-resters and precision shooters, because the shoulder does not move, it is erased, flattened etc..



F. Guffey

 

[F. Guffey]

“I suspect that might produce pressures high enough that the necks won't slip back and shorten the cases”

Not complicated but not as simple as the “shorten the cases”, the case gets longer from the shoulder to the case head, the case gets shorter from the shoulder to the mouth of the case, and that causes the case to shorten.

Heavy loads, I was forming cases for three rifles, I had little to no interest in doing it twice or beyond that times. I do not do reduced loads with Wheaties, Cheerios or any other cereal. I am the fan of cutting down on all that case travel, In the beginning I scribed the case body.shoulder juncture and the shoulder/neck juncture, again, the shoulder does not move, if it does the case stretched between the case head and case body. this brings us back to that part when someone is fire forming, no one ask “What receiver/rifle are we talking about?” There is more than one method and or technique for forming cases when different receivers are used.

F. Guffey

 

[black mamba]

I know that I accidentally (still not sure how it happened) loaded a 275 gr Hawk bullet in my 35 Whelen AI too long, and in a chrono string it measured 116 fps faster than the fastest of the other 4 shots (2399 jumped to 2515 fps). It couldn't have been too far into the lands, because it chambered just as easily as the others. But the recoil was noticeably more violent, and the bolt lift was quite stiff, although I didn't have to hammer it open. All loads were hand weighed and powder trickled, so the charge was the same as the others.

How much more pressure would be required to drive a 275 gr. bullet 116 fps faster? Many thousands of pounds I would think.

 

[mehavey]

The general rule of thumb is the cube of the velocity ratio. In your case that leads to a 15% pressure increase.

If I believe QuickLoad for the 35Wh_AI, I can get 2,400fps and very efficient burn out of a classic 35Whelan 22"
barrel using a full case of AA4350 for just under 50,000psi

15% above that is 57,500 psi (SAAMI max is somewhere betwenn 58 and 64ksi depending on your SAAMI reference
source). So w/o knowing anything else (your real load/barrel length, etc), I would not expect real problems
(brass flow into ejector slot) until you passed 70,000psi.

 

[black mamba]

Thanks, mehavey. The load was 57.5 grains of Alliant PP-2000MR, and the barrel length is 24". A fired case holds 73.8 gr of water. The offending load was supposed to be 3.30", but was somewhat longer seated, not sure how much. The bullet was 1.25".

 

[jepp2]

Range report

I had loaded up 10 rounds with the 0.025" into the lands. 2 each of 33.0, 33.5, 34.0, 34.5, and 35.0 gr of IMR 4895. All formed well, however the shoulder was sharper on the 35 gr load. I also included an image of the 100 yard target. Accuracy during forming was better than I expected, especially with the powder variation. All cases checked with paper clip, and no gap at all. There was only around 0.002 to 0.003" headspace on the new Win brass prior to firing.

Parent case is on the left, obviously. Cases start with the 33.0 grain to 35.0 from left to right in the picture.

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