Load work up in a ar10, lr308 Re: pressure ladder

[Gregg C]

Is this similar to looking for pressure with a bolt rifle? I originally assumed it would be, and figured I'd ask you folks that know these platforms.
I started with H380. Some folks allowed that to be too slow a powder... Well, I reckon it is. 500rds or so, discovered the bolt carrier had cracked.
So, new bolt carrier, and some BL-C2, going to start over.
Start low, roll up slow till flatter primers? That's what I do in a bolt gun......

 

[TRG65]

Loading a gas gun for precision has been frustrating for me. I've worked up two precision AR loads one in 6.5 creedmoor and one in 6 ARC. Tuning the gas block, buffer weights, and accuracy to get the load and reliability that I wanted was time consuming. Got decent loads for both and then after shooting the rifles in a couple matches each got the reliability/parts sorted out, but it took way more effort than bolt gun loading. I ended up in both cases with much lower velocity than I wanted.

 

[Gregg C]

I'm kind of expecting that. And, that's ok, for me, I have other hot rods I can pull out. It is amazing how much is involved in one of these platforms. When I started with it, I thought, No big deal....
Wow, was THAT inaccurate! It's fun, tho, cause I do like to tinker. I'm hoping the faster burning powder will be where I need to be. Thanks for the reply!

 

[budlight]

I have two 308 ar10's. I kind of cap them at 60K psi. I've found the most accurate are a few grains under max loads listed and I only use large rifle primers. NO magnum!

CFE 223, leverrevolution, and StaBall Matchare my go to. I use 125 TNT on pigs and 150's for paper and plinking.

I have quality bolts with roller bolt cam pins and rifle +2 inch gas systems. The +2 inch lowers the pressure enough that I use a standard micro steel block NON adjustable and typical 223 buffer weights .

 

[wwbrown]

Are you sure the bolt carrier cracked and not the bolt itself?

 

[Gregg C]

Are you sure the bolt carrier cracked and not the bolt itself?

Yeah I'm sure

 

[wwbrown]

Interesting, can you post pictures of the cracked BCG? I was surprised because I would not have thought the BCG was prone to cracks due to high pressure rounds, but I could be missing some causal relationship.

 

[Gregg C]

Interesting, can you post pictures of the cracked BCG? I was surprised because I would not have thought the BCG was prone to cracks due to high pressure rounds, but I could be missing some causal relationship.

Sorry, I apparently so no reason to keep it, as I can't find it. Sorry. I don't know that the PRESSURE was high, just running the action too hard. Also, maybe not super top end parts. I put one from KAK back in it, tho.

 

[Gregg C]

I have two 308 ar10's. I kind of cap them at 60K psi. I've found the most accurate are a few grains under max loads listed and I only use large rifle primers. NO magnum!

CFE 223, leverrevolution, and StaBall Matchare my go to. I use 125 TNT on pigs and 150's for paper and plinking.

I have quality bolts with roller bolt cam pins and rifle +2 inch gas systems. The +2 inch lowers the pressure enough that I use a standard micro steel block NON adjustable and typical 223 buffer weights .

Ball see too is right in there between Staball Match and CFE 223. SHOULD be good. We"'ll find out.

 

[Gregg C]

Oh yeah... Rifle length gas tube, carbine buffer( collapsible buttstock) , fixed gas block. Thinking pretty hard about a rifle length buffer, so I could slow the BCG down a little. Like to avoid adjustable gas block, tho, if possible.
I hear some folks talking about Varget,too. That's a bit faster burning yet, and not out of the question.

 

[budlight]

BL-C2 would be losing FPS and doesn't have the clean burning of modern powders.

I've seen a cracked BCG and destroyed cam pins from over pressure of large .090 gas port holes and carbine length gas tubes. Combined with heavy buffers and springs to get it to cycle right in 15's.

In 15's I use full auto bolts

 

[Zen Archery]

I can never run gas gun to bolt pressures.

 

[Gregg C]

I can never run gas gun to bolt pressures.

What should I look for? Ejection pattern, maybe?

 

[wwbrown]

What should I look for? Ejection pattern, maybe?

This is hard I find ARs in 308 show pressure signs early or at least different then bolt guns do. One example of the this is an ejector swipe shows up as soon as you get into moderate pressure, I have seen this with Lapua, standard Lake City, and M118LR brass among others and that is not soft brass.

I don't use adjustable gas blocks on AR-15 but find that they help on large frame, I think the gas port is oversized which provides great reliability with increased wear. Turning the gas down has helped ny builds.

Just my 2 cents,
wade