New AR, Bad Accuracy? (UPDATE: Good Accuracy!)

[mrvash]

Hey folks,

I've been shooting AR's and rifles for the past 6, or so, years. I don't proclaim to be an expert shooter, but medium-skilled; good enough to achieve good groups with the right equipment. However, I have recently pieced together an AR from parts of different manufacturers.

The rifle functioned excellently, it ran great without any issues, but the accuracy at 100 yards was terrible. It was almost like my zero was wandering all over the place, I was getting like 3-4" groups, this was the worst group I've ever seen out of an AR platform. Although at 36 yards I was getting consistent 1/2-3/4 groups. I was using American Eagle XM855, 62gr, green tip 5.56 and a Trijicon ACOG TA31 with chevron reticle. The barrel is a POF, 16.5" nitride heat treated, 1/8 twist, 5.56 with 5R-rifling, free-floated in a LaRue handguard.

I'm not sure if it was the ammo, me, or a combination of both, but it was disappointing. Maybe I'll buy better ammo, like 77gr Black Hill ammo, of Sierra MatchKings and try again later. Any recommendations on which ammo to try with this set up? Thanks!

[nate76239]

I agree try different ammo like the ones you mentioned also try AM Eagle 50 grain varmint tip and federal gmm 69 grain. Looks like a nice setup

[seal20]

What you got is an acceptable combat effective grouping using a combat optic and mil surp ammo.

[russ69]

What you got is an acceptable combat effective grouping using a combat optic and mil surp ammo.

3 or 4 inches with a 4 power scope and American Eagle ammo? Not great but totally believable.

[jarhead714]

Put a carry handle on it and see if you can maybe get it an inch tighter. A sling might help too...

[billped]

Double check the optic mount so you are absolutely certain it isn't shifting around slightly.

Other posters are probably right - that's what you get with that ammo.

[skyungjae]

That sounds about right. Were you shooting with a sandbag or any sort of rest?

[mrvash]

what in taking away from all the replies on here is that the ammo and optic used was probably not the best combination to max accuracy. I did double check the mount to ensure it was properly installed, which it was. I was using a bipod and an ammo can to prop up the rear of the rifle on a plastic picnic table, it felt stable enough and bolt rifles we shot from that same set up did fine. I forgot to add that I was using a Rock River 2-Stage trigger as well.

[newcitizen]

You mentioned you pieced it together, did you some how not torque something down right? Check your flash suppressor, does it have any abrasions or burs that could be scraping the bullet as it exits the barrel?

[.45 ACP]

M855 is 2-3 moa ammo from most shooters. Throw some Hornady SST or GMX in there and I would almost guarantee you will see 1 moa if you do your part.

[mrvash]

Maybe next week I'll buy better ammo and try again. Any recommendations on which grain of ammo and caliber, 223 or 556? I've been told that 1/8 barrels love 77gr bullets.

I did check the flash hider and it all seems good there. There were also no key-holing on the targets either.

[as_rocketman]

As others have said, 3-4 MOA is about the most you can guarantee with "field grade" ammunition, barrel, and fighting optics. My own AR-15 is a 2.5 MOA rifle, and it's good enough to do what it needs to do.

However, two obvious things to try -- is the optic secure? And, did you properly torque the barrel nut? Usually when an AR underperforms on my line, it's because of one of these two (or it's the shooter).

My go-to better-than-milspec ammo is Black Hills blue box. Easy to find and not too expensive. If this shrinks your groups noticeably, then it's the ammo. If no difference, then it's something about rifle or shooter.

[mrvash]

The optic was secured properly onto the rifle, and I was getting good, consistent, groups at around 36 yards, for zeroing, so I think everything was installed properly.

[19K]

3-4 inches with surplus quality ammo at 100 yards is normal.

[CandG]

XM855 are quality control rejects, usually they are only cosmetic rejects, but still... it is marketed as "less than perfect" ammo. So maybe that's part of it, have you used much of that same XM855 ammo in your other AR's? If it works well in your other guns, then it's probably not the problem.

The ACOG shouldn't be the problem, those sights usually hold zero extremely well, as long as it's mounted firmly, so double check that.

Are you able to swap the barrel out for a different one? That could help you rule out (or in) the barrel as the primary cause.

1/2 to 3/4" groups at 36 yards should translate to about 1.5 to 2.25" groups at 100 yards, so maybe the barrel rifling isn't properly stabilizing the bullet?

My last theory: Maybe nothing is wrong. If your "like 1/2in to 3/4in groupings at 36 yards" were actually a hair over that at 7/8", and your "like 3-4 inch groupings at 100 yards" were actually a hair less than that at 2.75", then that's exactly what they should be, based on geometry.

The easiest test, is run a magazine of match-grade ammo through it and see if you get similar results.