AR-10 loading question.

[joshb]

I have a DPMS SASS in 308 . I haven’t shot it in years. I pulled it out last week and started testing some loads with Sierra 168s . I loaded powders to the Service Rifle limits in my Hornady Manual. They mention their test loads were for M1As. I noticed the “regular” bolt gun 308 loads have higher load limits.
Where do the AR 10s strength limitations fall? Can it be loaded hotter than the M1A without damage?

 

[RegionRat]

@joshb it will depend on more variables than the parallel to AR-15 versus bolt guns due to the wide variety of barrel lengths and chamber standards, but the main drivers are barrel length, gas tube length, and port pressure.

If you think about it, bolt guns have none of those constraints but a gas driven semi auto must balance them all.

ETA: you will generally be constrained by what keeps the cycle happy as a priority. There are always exceptions but with normal choices for powders and bullets, you usually have a window between over and undergassed that should be wide enough to find what you like. You go past that to get to short term damage.

 

[Turpentine]

I shoot basically the same gun. While I do believe AR 10s can be loaded heavier than the m14/Garand style rifles, I do not think they should be loaded with full house bolt action type loads. OP rods were the limiting factor with m14/Garand designs. I think the actual bolt is likely the limiting factor in the AR 10. If your DPMS is over gassed, it can reek havoc on the bolt, receiver and other components when you use hotter loads. So some caution should be applied in my opinion. I load everything I shoot for mine and I prefer to use a more medium type powder in the Imr 4895 burn range because of port pressures. While this may not be totally necessary, it is my choice. There is absolutely no way I would use some of the loads worked up for my 700 in my AR.
Added: In my experiences, the AR 10 will let you know when you are getting on the warm side or have an out of balance system. Excessive bolt speed, excessive ejection distance, ejection angle, cratered primers (particularly with some DPMS firing pin hole tolerances), excessive recoil, extractor marks, plus your standard pressure signs on brass.
My DPMS craters primers badly. Even with very light loads. No puncture or rupture ever, no extractor groove, just cratering. But I was a victim of the bankruptcy and parts became difficult to find. I plan to replace the bolt or possibly have a bushing installed in the face. I understand that Adams Arms bolts will work. But not their cam pin. So I’ve been trying to run down some info on that.
I tried several bullets and different powders in this rifle. It does not like 150s at all. 165-168s are the ticket. AR COMP out performed every other powder by a mile in accuracy and consistency. 3-4 inch groups at 600 are not uncommon.

 

[joshb]

Thanks. I’m loading with IMR 4064 right now. I loaded up to 42 grains and stopped. That’s a little over the M1A loads. The best load at 40 grains gave me a 1” group at 100. I’m rusty, but I remember it shooting better than that. My load records from way back when are shoddy at best so I’m starting over.

 

[762plinker]

just remember you can tune your system
adjustable gas port
lighter spring on ejector/or shortened.
the truth can be seen in the original m118lr load.
developed for BOLT GUNS, when run in m14's the op rods dies,
and then began the death of a great load to be replaced with the 316
"good for everyone, great for no one"load

 

[Turpentine]

Would love to be around to see what that rifle can do. I spent a lot of time with mine and still do. It’s my favorite of all my ARs. Your SASS likely has the larger profile 18” fluted barrel And may even like the 175s. Mine has a hunter profile 20“. The second best powder in my gun was 4064. Around 42.8 grains in LC 85 match brass With 168s. 41.8-42 were close second. 42.8 is Close to Federals GM load. Though not a full house bolt action load As my 700 likes around 44 grains in LC Brass and 45.8 in win brass. Anything over 43 grains of 4064 was too hot for my comfort In the DPMS. My barrel is happiest at 2620 +/- fps. 41.5 of either 4895 was also decent. Around 42 of either 4895 was pushing it. Again this was in LC Brass. But nothing compared with AR Comp. With Winchester Brass 42 grains, Remington 41.7, and LC 67 or 85 Match 40.6 with 168 Amax‘s or Nosler 168 ballistic tips will do .5 MOA slow fire at 100. The best things I did to this rifle were add Geissele National Match trigger, SLR adjustable block and magpul prs stock.

 

[Ray123]

I shoot the same load in bolt guns and AR 10 in 308, & 6.5 Creedmoor, I use the high pressure small firing pin double ejector bolts in them, plus adjustable gas blocks to tune for the heavy high pressure loads...and have run 200 gr SMK to 2676 fps in a 18" AR 10 , single load... or 225 ELDM at 2477 fps.. same load in all bolt guns & ARs with longer barrels just get higher velocities than the 18" AR... but it's capable of over 3000 ft/lbs in 18" and excellent wind drift & energy for the small 308, with BCs of .715 & .777...

 

[Turpentine]

Thanks. I’m loading with IMR 4064 right now. I loaded up to 42 grains and stopped. That’s a little over the M1A loads. The best load at 40 grains gave me a 1” group at 100. I’m rusty, but I remember it shooting better than that. My load records from way back when are shoddy at best so I’m starting over.

What Brass

 

[joshb]

What Brass

I pulled the first bag of primed brass out of the drawer. It held 200 PMJ cases. I don’t remember where I got it but it was ready to go, so I loaded it. I have a lot of Federal and Lake City but it’s raw once fired.

 

[dantiff2]

Load for a 3 o’clock ejection pattern. Your rifle will be different from m1’s.

 

[Turpentine]

I pulled the first bag of primed brass out of the drawer. It held 200 PMJ cases. I don’t remember where I got it but it was ready to go, so I loaded it. I have a lot of Federal and Lake City but it’s raw once fired.

You are good. That’s why I mentioned all the different brass in my above post. LC and Federal will take less powder than Winchesters balloon headed case which was designed to hold more for Palma use at the time iIRC. 42.8 IMR 4064 in a federal or LC case with a 168 will come very close to duplicating the gold metal match although that number may move up or down slightly for different lots of powder. 41.745 is the mod 316 load
equivalent with 175s iIRC. The m118 Long Rang issue load was loaded with around 43.5 of Reloader 15. This load was found to be a bit warm in certain climates as R 15 can be a little too temp sensitive for extreme temps. IMR 4064 was found to be very good in varying temps and is actually pretty close to Varget. Varget is less temp sensitive but not by much and 4064 tends to be very accurate in 308.