Lithgow L1A1 SLR .308 load - excess pressure?

[David_S]

This is a companion post to one in "The art of the Rifle" where I asked about possible reasons for the robust ejection of shells with the L1A1 SLR. We test fired this rifle for the first time recently (with the standard peep sights) and found the shells ejecting up to 20ft from a prone position even with the gas regulator fully open. (Collateral damage?) Looking at the spent cases it seemed as if the primers were somewhat flattened suggesting overpressure. We also found it grouping poorly though it improved as we upped the load.

Reloading data

21" Barrel
New Lapua .308 cases
Winchester primers
ADI AR2206H powder (= Hodgdon H4895)
Powder charge 42.0 to 43.5gr in 0.5gr increments
Hornady 165gr BTSP seated to cannelure (LOA 69.8mm, 5.6mm off lands)

Results of 4-shot groups






Comments

1) Grouping is pretty disappointing for 50yard range but improves with increased charge. It seems to be coming off a sweet spot at 41.0 and approaching one at 43.5
2) Max velocity of 2,400 fps is low - we were wanting to get closer to 2,700fps which is the specified muzzle velocity for this rifle.
3) The primers seem rather flattened but all the primers looked the same regardless of powder charge.
4) The mouths of some of the ejected shells were flattened quite markedly by the vigorous ejection

Questions

1) Do the primers in the photo below indicate signs of overpressure or is this normal with a semi-automatic (we have not loaded for one before)?



2) If so have you any suggestions as to the cause and why all fired cases look the same regardless of powder charge?

4) Could these flattened primers be related to the vigorous ejection of the shells rather than the powder charge?

5) Is 2700 fps a reasonable velocity for this rifle. ADI's reloading guide gives a max charge of 43.5gr for a 168gr bullet with AR2206H which is why we stopped there. Their 24" test barrel gave 2,700 fps at max charge but we were nowhere near this. We would like to increase the charge to test for a sweet spot around 44.0gr

6) Would a slower powder such as ADI AR 2209 (=H4350) affect the pressure?

Any comments or suggestions would be appreciated as we have been a bit disappointed with this rifle so far.

David

[NuJudge]

I've shot a lot of 4895 in .308 rifles, and a good bit in an British L1A1 barrel. My favorite 165/168gr load in the .308 in all semi-autos is 41.5gr of either 4895, using Winchester primers, 165gr Remington SPCL or 168gr SMK bullets and LC brass. Accuracy results do get worse above that charge. My primers are a bit flat with 41.5 gr. At 41.5gr I am getting groups of about 4 MOA in the British barrel. Brass is found about 6 feet to the side, and a bit in front of me.

My LC brass may have less internal volume than your Lapua, perhaps giving me higher pressure than you.

Your primers don't look that flat to me.

Switching to 4350 is not the direction I would go with powder speed. What is causing your brass to get flung into the next ZIP code is pressure at the gas port. A "slower" powder (such as 4350) would raise gas pressure at the ejection port, increasing the distance brass would be thrown. If you are going to change powders, change to a "faster" powder. I don't find any difference in POI between the same charge of 4895 and 3031 with a gas operated .308, but there may be some difference in port pressure. Also, you might try reducing charge weight to lower port pressure: 4895 is very tollerant of reduced charges, and I've shot a lot of target .308 cartridges through M1 and M1A rifles that were as low as 36gr of either 4895.

I also have experience with shooting a Metric FAL rifle that has a larger than specification gas port in the barrel. The port was made larger to assure funtioning with a shortened barrel. You can measure port diameter by detail stripping that area of the rifle and seeing what drill bit sizes it will admit. It exhibits the kind of ejection you describe. In order to try and tame the distance it was flinging brass, plus reduce the damage to case rims, I got a new US-made spring for the gas piston that was stronger than the FN one, and got a gas piston that was worn to a bit smaller than FN's specification. Originally it was ejecting about 20 ft, now it is ejecting about 15 ft. It still heavily damages case rims during ejection. It might be possible for you to modify the vent aparatus, to have it vent more gas, but I have not studied how. I've decided to just shoot Berdan-primed surplus through it.

[Unclenick]

To get 2700 fps from a 24" tube with 43.5 grains of AR2206H powder with a 168 grain bullet seated to 2.800" (71.12 mm) COL, QuickLOAD says the case needs to expand to about 56.8 grains of water capacity on firing. That is within reason for a military or some of the heavier commercial cases fired in a test barrel (test barrels have minimum dimension chambers, like match rifles). If I leave that alone and change the barrel length to 21", the velocity drops to 2625 fps. A loss of about 25 fps per inch of barrel, which is normal for the .308.

If I then switch the bullet to the Hornady #3045 and COL to 2.748" (69.8 mm) respectively, the velocity changes to 2649 fps from 2625 fps. If I then open up the as-fired case water capacity to 60 grains of water to allow for a generous NATO chamber and the extra 0.030" freebore and add a little more powder moved forward with the bullet, I then get a prediction of 2564 fps which is getting close to what you report. It is running about 49,300 psi in the calculator at that point.

I don't know how close my modeling comes to your real experience without more information (actual case capacities as fired, in particular). So I hate to try to extrapolate to give you actual charge suggestions that exceed your manual maximum. I do show 2700 fps is just barely possible with the cartridge right at maximum rated pressure of 60,000 psi with 2206H, but all guns are individuals and that theoretical prediction may not work out in the real world. For now, 2625 seems to me to be a more reasonable maximum expectation.

Your ejection will get more vigorous loading up to that. Slower powder sustains pressure longer, so, as NuJudge stated, it will actually increase that ejection vigor if loaded to the same peak pressure, rather than reduce it. Keep in mind that NATO ball most often uses 147 grain bullets, or thereabouts, and their corresponding shorter barrel times will reduce the gas port pressure dwell.

The calculator suggests that if the other factors are correct, 41 grains of 2219 would give you similar velocity and barrel time to 43.5 grains of 2206H, but would drop gas port pressure 5-10% to reduce ejection force a little. I don't know how that comports with ADI's suggested loads for that powder and your bullet weight in the .308? The pressure peak would be a little higher and the charge won't fill the case as well, but should be acceptable.

[IllinoisCoyoteHunter]

Primers don't look flat to me. I use H4895 in my .243 win loads and found a load .1 grn over max load shoots the best. I am not condoning going over the max, but this is what my rifle likes.

[Slamfire]

Even though my data is with a 22” M1a and yours with a FN, these rifles were designed to fire the same ammunition.

I tested H4895 with an old standard which is the old military match 174 FMJBT. I compared my velocities with that of White Box match ammunition. That clocked exactly as advertized, 2550 fps.

I know that safe loads developed with the 174 can be used with 168 Match.

I received equivalent factory velocities between 40.5 grains and 41.0 grains H4895. You went up to 43.5 grains with a 165. That is way too hot for my components.

I like to keep 168’s between 2575 and 2625 fps in my M1a’s. Anything hotter just beats up the gun.

Your FAL, and I have a FAL, has an adjustable gas system. If you gas system, all the way open, is ejecting cases 20 feet, your pressures are high. Like crazy high. Ignore all those ideas of primer indications, primers lie, your over the screen velocities and ejection patterns ought to tell you something is wrong.

If I dialed my FAL gas system to full open, the rifle will not feed. I have played around with the gas system and when the loads are correct and the gas system is set two clicks above minimum, my cases fall within five to ten feet from a sitting position.

Cut your loads. That is my advice.

M1A 		1/10" 6 groove Douglas

174 FMJBT 40.5 grs H4895 wtd, lot 4501 LC mixed WLR 			
	 	OAL 2.800" 				
18 May 2008 T =  71 °F						
							
Ave Vel =	2524						
Std Dev =	36						
ES =	90						
High =	2587						
Low =	2497						
N =	5						
	good group						
							
174 FMJBT 41.0 grs H4895 wtd, lot 4501 LC mixed WLR 			
	 	OAL 2.800" 				
18 May 2008 T =  71 °F						
							
Ave Vel =	2594						
Std Dev =	14						
ES =	30						
High =	2609						
Low =	2579						
N =	5						
							
							
						
174 FMJBT 41.5 grs H4895 wtd, lot 4501 LC mixed WLR 			
	 	OAL 2.800" 				
18 May 2008 T =  71 °F						
							
Ave Vel =	2593						
Std Dev =	15						
ES =	42						
High =	2613						
Low =	2571						
N =	5						
	Best group						
							
174 FMJBT LC79 Match M118 White Box 					
18 May 2008 T =  71 °F						
							
Ave Vel =	2550						
Std Dev =	16						
ES =	41						
High =	2564						
Low =	2523						
N =	5

Wish I had a Lithgow FAL. Mine was made from parts. Imbel receiver Argentine barrel, ZA lower and South African buttstock. It functions fine but is not as accurate as any of my M1a's. A FAL is not a target rifle and service rifle barrels are not target barrels.

[David_S]

Thanks guys. There is a lot of excellent information in there and I appreciate the time you put into assembling it - what makes this forum worthwhile.

NuJudge - we will have a really good look at the gas adjustment system. I might get it checked out by a gunsmith to be sure. I can't see stronger gas piston return springs making a lot of difference though. I might try a reduced charge. My test firing indicates that at 41.0gr it is coming off a node or "sweet spot".

Unclenick - Thanks for running the data through Quickload - seems a neat program. I am more interested in accuracy than a specific velocity and from my first test firing it seems as if I should either look below 41.0 or just above 43.5.
How do you measure "actual case capacities as fired"? I don't have any 2219 powder but it is a good suggestion. ADI don't give any load data for 2219 and a 165gr projectile. The highest they go with 2219 is a 155gr bullet starting load 38gr and 2588fps and max load of 41.0 and 2710fps
Interestingly ADI state in their Handloaders' Guide that their AR2206 was "originally developed for the Australian Defence Forces 7.62mm" i.e. my son's L1A1. Their typical load for this powder is ".308 Winchester with 155gr jacketed projectile ...Charge Weight of 44.5gr and velocity 2,825fps". ADI state that the newer AR2206H has a burning rate only slighly slower than AR22206 and their typical load for it is also the .308Win and 155gr jacketed bullet, but 46gr and 2,873 fps.

Slamfire - you like to keep your 168s between 2575 and 2625 fps in your M1a’s but even my maximum load velocity of 2,540 is below this range which does not indicate excess pressure. No doubt there is excess pressure in the gas tube but this does not necessarily indicate excess case pressure.

IllinoisCoyoteHunter Interesting you have found your best load with the .243 just over the max. I have observed this with several of my reloads in other calibes and bullets.

What I think we will now do is to purchase a box of factory ammo and see if it shoots any differently - grouping and velocities, and whether the ejection is less vigorous - it is a real mission at the moment to find the spent cases. On the reloading side we will try some test loads with AR2206H both at the low end, say 39.0 to 41.5 and at the high end say 43 to 44.0 or 44.5 in .25 increments keeping an eye on pressures and velocities.

Thanks again guys
David