308 AR Build Accuracy Advice / Help

[aard3]

Hey Guys,

I recently finished a AR308 build that I have been accumulating parts for. Here are the specs

Black Rain Ordnance Matched Upper / Lower
Rainier Arms UltraMatch 20" Barrel
DPMS BCG
JP Enterprises XL Hand guard
AAC 51T Flash Hider / Break
Vortex Viper PST
American Defense Mount
Geissele SSAE Trigger

Took it out to the range yesterday and today, and I'm not very happy with the performance. Yesterday I shot all FGMM 168gr... today I brought out some more FGMM 168gr, FGMM 175gr, and Hornady 168gr AMax. I even brought some reloads with me...I also had another shooter I trust verify my results.

Best I can do with it is about a 1.5" group, and that's being "generous"... most of the groups are about 2". I wasn't expecting it to be 1/2 MOA gun, but I was hoping to at least be MOA.

I haven't contact Rainier Arms yet (I'm sure they will take care of me), because I wanted to reach out the the SH community and make sure my expectations were reasonable and see if you guys had any advice for other things to try first.

So there it is, is there anything in this build that I should look at? BCG? Muzzle Brake? etc.

Rifle headspaced out OK, I did notice that the chamber is pretty tight.

The JP Handguard install was different, I torqued it to what they called for.

Any advice?

Thanks!

 

[biner626]

Re: 308 AR Build Accuracy Advice / Help

How many rounds through it? Did you clean the barrel before shooting it for the first time?
Try a different optic/mount.
Check the gas tube alignment.
Take off the muzzle device and try again.
Do these independently so you know which to blame.

 

[aard3]

Re: 308 AR Build Accuracy Advice / Help

40 rounds the first day (all 168 gr FGMM)
52 rounds the second day (mix of the different types)

Dewey guide rod and jag with bore guide. I just ran a patch with a small amount of oil on it after I built it, just to check for any residual much... didn't aggressively clean it with a brush or anything.

After the first day, same procedure, used some sweets on it. Ran patches until they were relatively clean.

Good call on the optic/mount. This was my first experience with the ADM mount, I'll try a optic with some seekins rings next.

Gas tube "looked" fine, but I'll double check.

I'll try the muzzle brake too... I didn't think about this.

Thanks for the advice. Besides the fact it's not a shooter, the gun functions flawlessly. I'd really like to figure this one out though!

 

[biner626]

Re: 308 AR Build Accuracy Advice / Help

The gas tube shouldn't wiggle when the bolt goes home. If it does then its misaligned. I doubt it alone would throw groups like that. The ADM is a great mount, but, anyone can have a bad day. If it's the optic then CS at Vortex will help you out. My bet is on the brake or the crown. Good luck.

 

[Temp9]

Re: 308 AR Build Accuracy Advice / Help

Double check that there's no contact between the handguard and the barrel, gas block, or gas tube. Unless you have prior experience shooting precision AR's, don't rule out the shooter. They're very picky about needing everything to be done right. Get another shooter to test it, if necessary. Swap out optics to a known performer and test again.

Your expectations are perfectly reasonable. That barrel should hold sub-MOA 5-shot groups with good ammo and a good shooter.

 

[Boss334OP]

Re: 308 AR Build Accuracy Advice / Help

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Temp9</div><div class="ubbcode-body">Double check that there's no contact between the handguard and the barrel, gas block, or gas tube. Unless you have prior experience shooting precision AR's, don't rule out the shooter. They're very picky about needing everything to be done right. Get another shooter to test it, if necessary. Swap out optics to a known performer and test again.

Your expectations are perfectly reasonable. That barrel should hold sub-MOA 5-shot groups with good ammo and a good shooter.</div></div>
+1 Gas guns are a different beast altogether.

 

[LongArm]

Re: 308 AR Build Accuracy Advice / Help

Is it over gassed? Where to the cases fall, they should be falling around the 4:30pm mark or to your lower right side.

 

[BCP]

Re: 308 AR Build Accuracy Advice / Help

What do the groups look like? Is it a shotgun pattern or is it a good group with a couple fliers, or two groups in one?

 

[Danhalen7.62]

Re: 308 AR Build Accuracy Advice / Help

Over pressure is a big issue w/ ar10's and accuracy... After months of trial and error, I load mine lean to achieve a good grouping.