Approaching maximum loads in a milsurp - safety advice.

[pathdoc]

Just thought I would ask people's advice about this, as I'm about to plunge eyeball-deep into serious load development for my .303, as opposed to just tinkering and getting my toes back in the water after an absence.

I offer as an example the starting and maximum loads for the 180gn RN Speer bullet in this calibre with Varget - 37gn and 41gn (14th edition). It occurred to me that IF one were loading for velocity (which I'm not, but let's assume I were), one could probably try 37gn, 38gn and maybe even 39gn in three discrete jumps and be pretty safe if there were no pressure signs at the previous load.

But after that, what? Would anyone here be game to go straight to 40gn, assuming velocity was the only object? Or would you all be loading a couple at 39.5gn to make sure of yourselves first, perhaps even a few at 39.7? And having hypothetically got to a grain below maximum without issues, how slow would you creep up after that? Naturally the safest thing to do is to go up in 0.1 grain increments, but is this being over-cautious? Or would you only start to be that careful within a half-grain of the top?

And out of interest, would loading for a strong, front-locking modern action change your approach at all?

It goes without saying that every charge would be check-weighed, even if it came out of the best powder dispenser on Earth.

 

[steve4102]

I would go in .5gr increments.

if there were no pressure signs at the previous load.

The 303 runs at 49 K psi, what pressure signs would you be looking for and at what psi would you expect them to appear?

 

[mehavey]

load development for my .303

If you're using an SMLE, I'm start looking at action/brass stretch long before before brass flow.

 

[Slamfire]

I develop my loads with a chronograph and I shoot factory loads to determine a base line. The 303 British is not a hot round, I have heard numbers like 44,000 psia, not anything approaching 50 Kpsia.

The basic problem with the Lee Enfield is that it is a rear locking action. From what I can tell, the material is plain carbon steels so it does not have as high a yield as an alloy steel. You push that action too hard and you will get case separations quickly and you are weakening the action. Something that is not appreciated is that no rifle was every built for an infinite service life. Typically these are expected to be light duty, which means the thing will be worn out in 10,000-15,000 service cycles. So, if you shoot rounds that are within design parameters you will get a normal service life. If you push beyond design loads the service life drops.

It is worth going over to this thread, which was about the top strap of a SuperBlack Hawk blowing off, and looking at the chart and text that was posted.

http://castboolits.gunloads.com/showthread.php?150409-Ruger-om-44-convertible&highlight=convertible

A few good quotes from the thread:

1) Firearms in general (the type we plebeians can get our mits one) are not designed for infinite fatigue life.

2) The Factors of safety used in firearms design are in line with low end of fatigue requirements (usually less than 10,000 cycles).

3) One of the funny things about fatigue is that each time you push the material past its original design point, you lower its expected life.

4) I am looking at this as an older gun with an unknown number of rounds through it. but based on its age a substantial round count seems likely.

5) When these firearms are designed it is generally preferable for something else to go before the cylinder lets go and takes the top strap. Generally this takes the form of the gun wearing loose or the barrel wearing out. But they are designed to handle X rounds at standard pressures.

6) I see alot of folks calculate the strengths of Rugers, but these calculations are only ever performing an evaluation on a straight static pressure basis. This is wrong when trying to determine if a load is safe.

I attached a couple of marked up figures for your perusal

Now this is the velocities I got out of my No 4 with factory ammunition. The round is not that hot.

[SIZE="3"][B]No. 4 MkII mfgr 12/53[/B]			
 						
174 Greek Ball HXP 70 				
			 			
	9-May-92	T ≈  70 °F				
						
Ave Vel =	2488			 	 	 
Std Dev =	12			 	 	 
ES =	27			 	 	 
Low =	2473			 	 	 
High =	2500			 	 	 
N =	5			 		
						
						
174 grain Greek Ball HXP 70				
					 	 
8 Feb 2012 T =  50 °F 				
						
Ave Vel =	2423					
Std Dev =	14					
ES =	53					
High =	2456					
Low =	2403					
N =	14					
						
						
180 grain Winchester Silvertip Factory Ammunition		
					 	
8 Feb 2012 T =  50 °F 				
						
Ave Vel =	2297				 	
Std Dev =	14				 	
ES =	46				 	
High =	2319				 	
Low =	2273				 	
N =	10[/SIZE]

 

[wogpotter]

When approaching max I go 3/10 gr & work from there. My chronograph shows a 25 FPS increase per 3/10 gr increase with 150 Gr bullets in my full length No4 Mk2. Maybe drop to 2/10ths Gr with the 180?
I load just 10 of each set so if I do find pressure signs I can pull any "iffy" loads without undue drama.
As for the front/rear locking I've never found it to be an issue. More important is small increments & look for pressure signs.

 

[Clark]

Steel does not get add fatigue until it is within ~ 30% of plastic deformation.
That is millions of stress cycles out.
That is, I guess, why SAAMI proof pressures are ~ 30% over max average.
From "Handbook for Shooters and Reloaders Volume II" P.O. Ackley 1966..
When Ackley tested the 303 Brit he got a leaky primer at 52 gr 4198 150 gr [I estimate that at 117 kpsi with Quickload].
When Ackley tested the 303 Brit he got a wrecked bolt and bent receiver at 50 gr 2400 150 gr [I estimate that at 175 kpsi with Quickload].
My general opinion of gun writers is that they prey upon low information consumers and just type anything that comes to mind that will appeal to their audience.
However, with Ackley, I have never found him making up any BS yet.
He says of the 303 Brit action, it is stretchy.
When I calculate the stretch of the action and measure the stretch of the 3030 brass, he was right!!
A gun writer that was not just BS!!
Ackley II 1966 page 13:
"The locking lugs themselves did not give way.
The whole action appeared to have plenty of strength except for this
one characteristic, which allows too much spring in the bolt and receiver."
My calculation:
The rim of a 303 case is .064" - .010"
The chamber rim of a 303 is .064" + .015"
That is .025" slop on the headspace of the rim.
The same story for the shoulder = .025" slop
Total mismatch effect of should and rim on case and chamber meeting at shoulder = .050"
The No 4 rifles have .19" firing pin holes and .58" OD putting the cross sectional area at .23 sq. in and the compression length is 4.2"
movement = [Force] [ length]/[[area] [modulus]
movement = [chamber pressure][case ID][length]/[[area][ modulus]
movement = [ 60 kpsi] [.107 sq. in][4.2 in]/[.236 sq. in[30 M lb/ sq. in]
movement = .0041" @ 65k psi chamber pressure
movement = .0038" @ 60k psi chamber pressure
movement = .0029" @ 45k psi chamber pressure
movement = .0019" at 30k psi chamber pressure
So to compare case stretch caused by bolt springyness to chamber fit, .004" max to .025" max.
But to compare case wear caused by bolt springiness to chamber fit, .004" max to .050" max.

 

[HiBC]

I do not own a SMLE,have no experience with one.

I suspect there will be a point where you will see an increase in case stretch,and it follows,a decrease in useful brass life.

Check for a stretch ring (brass thinning) with the bent paper clip trick.

Generally,"looking for pressure signs" as a boundary is about looking for approaching cartridge case failure,brass flow into bolt face,loose primer pockets,sticky extraction,etc.The assumption is the rifle has a reserve of strength,and,in modern design strong actions,the brass is the weak link.

No disrespect to the SMLE,it came from a different era,and has a lower design limitation.

"The edge" is in a different place.

Accuracy and case life are important priorities.I suggest do not exceed book max,and use a chronograph ..You might consider targeting original,mil spec performance as your max goal,with a willingness to compromise lower.

Its good if the load calibrates to the sights.

 

[mikld]

I have a .303 British (Savage No. 4 Mk I*) that I'm reloading for. I have absolutely no need/want/desire for shooting upper range reloads in this rifle. The Lee-Enfield isn't a real strong action; small bolt with rear locking lugs and accurate ammo usually isn't achieved at near max. loadings. If I were to want a "faster" higher velocity .311 bullet, I'd choose a different gun...

I would suggest starting with the starting loads and load for accuracy. Go up .5 grains at a time then .2 when a load looks promising.

 

[mehavey]

No disrespect to the SMLE,it came from a
different era, and has a lower design limitation.

The SMLE was deliberately designed with an incredibly fast-cycling rear-locking bolt. That speed came with the price of putting the action's rails under stress instead of the forward pressure ring.

Like the Stoner/M16 design, it was a compromise, but perfect for its intended military use.

Of the 303s, [My] P14's forward lugs make brass flow the past-critical sign. With an SMLE significant brass stretch occurs much earlier and is its critical sign.

 

[pathdoc]

Thanks for the advice and input so far, everyone. Pressure signs being sought are the usual classics - sticky bolt lift, hard extraction, extractor/ejector marks, primer flattening, etc.

My previous experience with SMLEs has been for the group sizes to shrink and then open up again at least a grain and a half before maximum was reached. I'm well aware of the case-life issue with these rifles, and current cases are being strictly neck-sized only, with the exception of brass used in previous SMLE chambers which is getting one full-length pass before changing guns.

I'm currently about to try an OCW-like load development exercise, and praying I find something good in the lower half of the charge-weight range for the reasons some of you have already touched on. If I don't, I'm resigned to proceeding very carefully into the upper half and seeing what happens. The OCW method supposedly relies on being willing and able to go one step over absolute maximum, but there's no way in hell I'm doing that.

http://optimalchargeweight.embarqspace.com/

Charge weights for the 180gn Speers are ranging from 37 to 39gn at 0.4gn increments; for the 215gn Woodleighs, from 36 to 38gn (max 39.5) in the same increments. The bullet that performs the better in both tests (and whatever further testing comes out of them) gets the nod on D-day.

The action is a 1945 Lithgow, so it almost certainly missed both world wars (or at least the majority of the second) and might even have missed Korea if it was lucky. Fatigue life should be fairly low from that POV. Sight is a scope for hunting, so trajectory matching isn't important.

Slamfire, re. your point about using factory loads as a guide to pressure - this is not necessarily a good indicator IMO unless you know exactly what they're loading with. They may have access to something giving less pressure for similar velocity to commercially available powders, which could leave you in a very bad place. For example, when they changed over from the original compressed black powder pellet to cordite, they lost 2200psi of breech pressure and gained 120fps or so.

I really don't want to go much beyond midrange loads if I can possibly help it - but I don't want to limit myself to that if a massive improvement lies somewhere a little further up the power scale.

 

[wogpotter]

I've usually found about 100 FPS below max is a decent "sweet spot".

 

[HiBC]

Just to make sure the point is clear,the pressure signs you mention would indicate,IMO,well past 60,000 psi.That is approaching the edge for the strong designs like a Mauser 98,Springfield,M-70,Rem 700,etc.

Those signs are well beyond what is OK for an SMLE.I suggest you not load to those pressure signs.

 

[Clark]

The 303 Enfield is plenty strong, it just stretches the brass at low pressures.
The brass is rimmed so it is much stronger than 308 brass, but the brass will not live long getting stretched.
I have a Ishapore 2A1 rifle that shoot steel cased Bulgarian surplus 7.62x51mm NATO surplus the best.
I have always thought that has something to do with the stretchyness of the action. The steel case may be thinner, but it can stretch further before plastic deformation.
I have a 1917 Sav99 that locks up in the rear. I put a 6mmBR barrel on it. At 85kpsi the brass stretches.
I have got to the point, I do not want to play around with brass stretching.
If I were to reload, I would load the 303 Brit wimpy with slow powder.
The military loads are too hot for long brass life.

 

[Unclenick]

Stretching is common for all rear lug designs. M. L. McPherson likes to use case growth as a pressure limit indicator on lever guns, the Marlin 1895 in particular.

For those not familiar with the subject, for a given amount of stretching (tensile) force applied to an elastic material of uniform cross sectional area, the material will stretch the same percentage of its length, regardless of what that length is. If a one inch length of steel of a given cross-sectional area is stretched one thousandth of an inch by a particular tensile force, then a 5 inch length of the same material will stretch five thousandths of an inch under that same force. Since stretching force is applied between the breechface and the locking lugs of a rifle, it follows that the more distance there is between the lug locking surfaces and the breech face, the more stretching there will generally be. This is before taking varying cross-sectional areas into account.

Infinite life is unlikely for firearms for various reasons. The yield point used in this country is a force per unit cross sectional area that causes 0.2% permanent deformation. At some lower pressure the permanent deformation will be just 0.1%. This is what the Brits use as the definition of yield point, also called the proof point for reasons you can guess. But if you want absolutely no permanent deformation, the steel has to be operated within what is called the true elastic limit, where no measurable deformation occurs; where it behaves like a perfect sprint. In the one civil engineering class I took in school, if I recall correctly, a safety factor of 15 times smaller force than the yield was used. A bridge, of course, can actually see tens of millions of stress cycles from fully loaded semi's, depending where it is located, and no accumulated deformation over time is acceptable.


Pathdoc,

A couple of usual rules of thumb are to take charges up in increments of 2% the expected maximum when looking for pressure signs. This takes you from -10% to maximum in 6 shots (starting load + 5 increments to maximum). That will typically produce about 4-6% increase in peak pressure per step, depending on the load and powder and that's close to the standard deviation SAAMI allows for pressures in its system (4% for rifle and 5% for handguns), and so is a good significant pressure step size. When you spot a pressure sign while working up through charge increments that size, you back the load down 5% (typically a 10%-15% peak pressure reduction) to stay clear of that symptom in the future.

Incrementing loads for accuracy is another matter and requires smaller steps. I think Dan Newberry's use of 0.7%-1% makes sense. I use 0.7% or 0.2 grains, whichever is larger, as a ±0.1 grain precision scale can't reliably produce smaller incremental changes.

 

[pathdoc]

I suggest you not load to those pressure signs.

In that case, no offence, but what the hell have I got left to go on? I've already said I intend to stop at book maximum whatever happens. As for a chronograph, I'm really not sure what that's going to show me. Most chrony data supplied in reloading manuals aren't taken at temperatures below zero celsius, which is the sort of weather in which I expect to do most of my shooting. Bear in mind also that the factories' figures are all from specific combinations of primer, powder and case brand which might not apply to me, especially since the brass they use is almost certainly virgin factory stuff straight off the line and most of mine is previously fired in an SMLE chamber (notoriously spacious) and neck sized only.

If there's any reason AT ALL for me to use a chronograph, it's to determine what's happening downrange - and for that I can always bring the targets back to 50yd after sighting-in at a hundred, determine how my impact point changes and back-calculate my trajectories from the known scope height and published G1 BC.

My previous experience with a chronograph gave me figures exceeding maximum velocity from a minimum book load. As far as I'm concerned, they're no guide at all to how hot things are running.

Edited to reply to unclenick:

Thanks for the pressure discussion. As far as the increments go, with "book" maximum charges running in the neighbourhood of 40 grains of Varget for both bullet types I'm trying (39.5 for the heavies, 41 for the 180s), 1% gives me a 0.4gn increment - which is what I'm using. I could always go back and fill in the 0.2gn gaps if I've got nothing to do sometime this week, I suppose...

 

[Unclenick]

I think he just meant those particular pressure signs were ones he associated with higher pressures than your gun is made for, and in guns with front locking lugs, he'd be right. But with your rear locking lugs, the case can stretch more at lower pressures, and then the steel will spring back, trapping the over-length brass and causing sticky bolt lift also at lower pressures. I'd watch for the stickiness perhaps not to be quite as hard because of the greater span of steel. In lever guns, that extended brass often won't let the bolt close completely again after opening, and that would be a good second check for you to make if you are unsure whether the lift felt like it was rubbing too hard or not. Look at my list of pressure signs I linked to and at numbers 9 and 11 in particular.

 

[Jim Watson]

Ken Waters routinely estimated chamber pressure by casehead expansion.
The internet says you can't do that, but he didn't seem to blow up many guns.
I would just get out my copy of Pet Loads and go with Ken instead of theorizing.

 

[mehavey]

I like Uncle Nick's case-stretch/chamber-bolt jam. It's the ONLY sign
that I see associated w/ the action's early overpressure/reaction mode.

 

[Slamfire]

As for the Lee Enfield surviving 175 Kpsia, numbers that are spit out by computer programs may not reflect reality. I wrote programs, decades ago, (in FORTRAN) and the formulas used are only as good as the data used to create the equation of state. Predictions outside of measured data are not reliable. I am unaware of any cartridges that operate at 175 kpsia and I am skeptical of any computer result that says that is the real pressure unless there is measured data to support the prediction. But, even more so, just what is the burst strength of a cartridge? That 303 Brit cartridge has some case head unsupported and I highly doubt a brass tube of about 0.04" (SWAG) of quarter hard brass is going to be intact at the crazy pressures Quickload is predicting.

In the one civil engineering class I took in school, if I recall correctly, a safety factor of 15 times smaller force than the yield was used. A bridge, of course, can actually see tens of millions of stress cycles from fully loaded semi's, depending where it is located, and no accumulated deformation over time is acceptable.

Safety factors depend on the application. The lifetime of a bridge can be centuries. One incarnation of London bridge lasted 600 years. Firearms are not expected to through centuries of constant use, weight considerations are more important than extended lifetime. Any fool can design and build a 90 lb rifle which due to massive overdesign, the action will last forever. It takes smarts to build something that weighs 7.5 pounds and operates in all environments without breaking for 6000 rounds. If you notice, 6000 rounds is the average test life required by the military for firearms procurement. You don't need massive safety factors for that. If you look at Brassey's and the few firearm design books, a 2:1 safety factor is used on locking mechanisms. That is it. That does not mean the mechanism is twice as strong as it needs to be, it means given the uncertainty of cartridges, materials, tolerances , a rifle built to a 2:1 safety factor will probably shoot for 6000 rounds without breaking. Even cannon design has its limits. I talked to a cannon designer, the 155 used on the Stryker, after 15,000 rounds, everything, the barrel, breech mechanism, the carriage, is scrapped. Military arms, big and small, do not have indefinite lifetimes, nor are they expected to have indefinite lifetimes.

My previous experience with a chronograph gave me figures exceeding maximum velocity from a minimum book load. As far as I'm concerned, they're no guide at all to how hot things are running.

There is no free lunch. Bullets don't go faster with lower pressures. I am of the opinion that if velocities exceed book values, regardless of the charge level, you have exceeded a maximum load. That is why I use a chronograph. Just keep on increasing the charge and you will have sticking extraction, blown or pierced primers, or in the Lee Enfield, case head separations.

 

[mehavey]

previous experience with a chronograph gave me figures
exceeding maximum velocity from a minimum book load.

Building on Slamfire's note above, if you are getting that kind of reading, something's wrong.

At that point I would stop, and reconsider how/why either the chronograph is providing
erroneous data, or why the cartridge/firearm system is reacting far out-of-spec.

(Actually, the first thing I'd do is fire a known commercial load and compare numbers.
If the chronograph then reads normally, you've got a bigger problem....)


~~~~~~~~
Handloading development without a chronograph is akin to flying blind.
Handloading development without an internal ballistics program and/or pressure trace is then covering up the instrument panel