Loads for an Armalite AR10 .308T

[DamonGettier]

I need help with a load. I just bought a new Armalite AR10 .308T and did the break in thing yesterday...1 shot, clean, 1 shot, clean, etc for 10 shots. Shot my first 5 shot group and it was horrible. The group was about 2 inches. I have way too much money in this rig for this type of performance. I have it topped with a Leupold 4.5-14x50mm AO. The twist is either a 1 in 11 1/4 or 11 3/4. Any help as to load would be appreciated.

Thanks

 

[Klong]

My DPMS likes the 175 and the 180 SMK bullets with a near max load of 4064 or 4895 and match primers. What is the twist rate on your barrel?

 

[DamonGettier]

11 1/4 I think.

 

[Spotcheck_Billy]

11 1/4 I think.

Better check it. My AR10,T) bought NIB has a 1/10 twist!

A nice easy accurate load - 168SMK, 41.5gr. H4895, Win brass, WLR primers, COAL 2.80"

Good luck with it

 

[Dans40X]

My ArmaLite likes moly'd 155's w/43gr of IMR4064 in Lapua brass,Fed 210 primers @2.850 OAL

 

[overbore]

What you MUST Be cautious with is chamber presure as you are dealing with aluminum not steel. Cross check your loads against suggested pressure loads from say Hogdon. I suggest moly 155's as they genrate lower chamber pressures.. Overbore

 

[Spotcheck_Billy]

What you MUST Be cautious with is chamber presure as you are dealing with aluminum not steel. Cross check your loads against suggested pressure loads from say Hogdon. I suggest moly 155's as they genrate lower chamber pressures.. Overbore

I have no objection to your point about being cautious with chamber pressure. That should be a given when working up loads with all firearms.

However, as a Colt certified M16/AR15 LE armorer I must respectfully take issue with your statement "you are dealing with aluminum not steel". On the AR- pattern firearm the steel bolt lugs lock directly into a steel barrel extension that does the same job of the bolt lug recesses in a standard bolt action rifle. All that the AR aluminum reciever does is to provide a housing for the steel bolt/carrier/barrel extension/barrel group. Aluminum does not figure into the equation at all as far as action strength or pressure handling capabilities are concerned

 

[gunor]

If your AR-10 does not shoot either the 168 or 175 SMK with a load of 41 to 42 grains of 4895 well, then you have issues.

Issues include a bad barrel, shooting technique, or scope.

The above load is an extremely common load that has worked in many guns,Match grade M-1A or M-14 - and others), and more than likely shoot well in any properly chambered and barreled 308 rifle, whether the barrel twist is from 1-10 to 1-13.

My 2 cents.

Geoff in Oregon

 

[overbore]

Spotcheck Billy: Sir,
Since you do in fact have greater expertise with this arm what chamber pressures do you suggst as the upward limit? I trust you are not into 62,000psi as an ultimate strutural/fatigue point. I limiit mine to 52,000 to keep things well into the "green" as I have ample bolt guns for exploring the upper pressure ranges. Thanks, Overbore

 

[Spotcheck_Billy]

Overbore,
Standard issue military ammo manufactured for the AR-platform firearms normally exceeds the upper pressure limits as listed by SAAMI. The military issue ball and tracer rounds are spec'd out at 55,000 psi. The high pressure test, or "proof" rounds measure 70,000 psi.

As shown, 55,000 psi chamber pressure is absolutely safe in these weapons if the ammunition matches the chamber dimensions. Highpower and Service Rifle competitors quite often exceed that figure. They commonly load until they encounter the primers falling out and then back off one half to one grain and call it good, whatever that pressure might be! I doubt that any of them have the means to accurately measure the chamber pressures that they develop using this method, and any guesses are just that, owing to the differences in brass, etc. You might check the volumes written by Zediker, Feamster, or Martin&Tillman for elaboration on this subject.

Note that I do not advocate this practise. I'm only reporting on what has become SOP for this shooting discipline. I have no way of measureing true chamber pressures and won't fool myself by thinking that I can. When working up loads for these rifles I will normally stop when I notice a slight amount of extrusion around the firing pin mark on the primer and back off on the powder charge accordingly. I try not to be a hero and do not advocate loading to high chamber pressures,like 62,000 psi) because that's just tempting fate IMO, even on a bolt gun

 

[BillK]

The biggest issue with the AR style guns is the pressure on the gas system. I luckily have not had problems but too much port pressure,usually caused by slow powder)can possibly break extractors rip off case rims etc etc. You have to remember the Stolle Panda action kinda copped some of their stuff from the Stoner design. The biggest difference is one is gas operated and the number of lugs/lug design.

 

[overbore]

Spot Check Billy,

That was a great post with just the specific techno stuff we all need. I will only loosen primers in my 308 bolt gun shooting 190gr bthp's and appreciate your 55,000psi reference point. Any recoil buffer found useful at those loadings? Many thanks and well done.
Cordially, Overbore Member Revolutionary War Vets Association

 

[Spotcheck_Billy]

BillK,
The common problem is usually not the pressure measurement itself but it's usually that the gun gets too much gas too fast. Usually occurs when the powder speed is not correct for the bullet weight and/or the gas port diameter/placement is not appropriate for the barrel length etc. I've found that staying between H322 on the fast side and BL-C,2) in the slower end of the burning rates yields excellent loads with bullets from 52grs. to 80grs. in the .223 cartridge and 125grs. through 175grs in the .308 round. My favorite powders are H335, mil-surp WCC844, H4895, Varget, and Re15. Never run into any problems with those powders when the proper bullet weights are selected.

overbore,
Are you asking about the use of an aftermarket accessory recoil buffer? I never use them. They're not needed. There are a series of factory buffers available in different weights. The standard weight buffers are good-to-go in standard rifles under normal conditions. Heavier buffers are usually used in carbines, especially for FA use. Most experimentation is being done with heavier bolt carriers and add-on carrier weight systems to slow down the bolt and smooth out the recoil pulse in competition shooting. That type of modification has to be worked out on each individual rifle on a load-by-load basis.

 

[overbore]

Spot Check Billy, One again thanks for your expertise. We are close together in our independent conclusions about powder as I learned my gas pressure considerations first on M-1 then the M-14. My AR is in 300wsm flavor with a custom Kreiger and I have optimized things with 155gr molly Mk's and Varget as my belief is that these are very good weapons that should be used but not abused-- unless the flag goes up. Well done, Sir. Cordially, Overbore
Member, Revolutionary War Veterans Assoc.