What to make of this grouping with an AR-15 & FGMM

[jlow]

I was testing the accuracy of an AR-15 today.

To take the ammunition out of the equation, I shot 10 rounds of new FGMM at a target 100 yards away. The gun has a chrome line 16” barrel with 1:7 twist. A high power high quality NF NXS 8-32x56 scope mounted on a LaRue LT-104 mount was acquisitioned for the test – at that magnification, the X ring of the target was clearly visible and there was no problem aiming and maintaining an aim on the X. All scope mounts were tight or loctite in place. The gun was mounted on a Caldwell Lead Sled DFT Rifle Shooting Rest so that there was minimal shooter induced movement. There was basically no wind.

Five rounds were clustered close together as one would expect for this type of quality ammunition, but the five other rounds were scattered to the lower right. The grouping size was 2.034 MOA as measured with the OnTarget software.

My question is what could be causing this type of extreme spread, is it the barrel? Seems like all other variables have been taken out of the equation.

 

[dareposte]

Re: What to make of this grouping with an AR-15 & FGMM

Looks like about par for the course for a mil-spec chrome lined bore in my opinion.

If you want ragged holes from an AR you need a premium barrel. In AR's this seems to be generally accepted, even the DMR's use premium SS match barrels from Krieger or RRA to get there. I'd recommend a barrel from one of those two, or Lilja, Noveske, Shilen, Pac-Nor, or a few others I'm probably forgetting.

Some owners get lucky and find one that shoots well with a standard barrel but I believe that is the exception and not the rule.

 

[jlow]

Re: What to make of this grouping with an AR-15 & FGMM

I guess going into this test, my own suspicion was along the same line and actually the reason for the test. The only slight hesitation I had was due to seeing the tight group from those 5 rounds and not a general scattering.

In general, I am indeed leaning on replacing the barrel. I am reasonably handy and have in fact taken an AR-15 armorer course and taken this gun completely apart and successfully put back together. Generally looking for a modest weight match barrel between 16-18” long but a bit daunted by the choices out there.

Right now looking at a White Oak SPR Match Barrel as I shoot out to 600 yards with this rifle but do want to keep it relatively light.

 

[dareposte]

Re: What to make of this grouping with an AR-15 & FGMM

White oak is reportedly top notch but I've never had one personally. I'm usually OK with 2 MOA groups from my AR since that's about as good as I can reliably shoot with open sights / 1x mag and meets my desire for that type of rifle.

I believe the current barrel being supplied on the DMR rifles is a Douglas 1:8 twist stainless. It's designed to shoot the 77gr match bullets.

Was there any "Stringing" of the group as it formed? Did you notice that all the 5 together were shot and then a shift occurred, or was it relatively random? It could be barrel heating, bolt lock-up, fouling, or stock contact. Is this rifle free-floated?

 

[sardiniagunner]

Re: What to make of this grouping with an AR-15 & FGMM

I would repeat the test again to validate my results. Look for a clump of shots in the same place that you got them in this test. If they dont reapear then they may have been random.

Next thing I would do is swap out the scope and mount (although that combo seems above reproach) and repeat the test to see if that changes things.

Another thing that helps out is to be shooting through a chrono. I know thats anal but it eliminates another variable. that ammo shouldnt move around on you velocity wise, but just today I was out shooting some groups and testing loads and I watched a round deviate from the rest in the group by 100 fps and it fell out the bottom of the group. That told me two things. One is that that ammo is a little suspect. the other is that I didnt inadvertantly pull that round low.

Bottom line?

You need a larger body of evidence before you convict this barrel of the crime of sub par accuracy.

Of course dont let that stop you from slapping a primo barrel on that thing if that what you want to do

 

[jlow]

Re: What to make of this grouping with an AR-15 & FGMM

Thanks for the feedback!

Yea, I admit I am a bit on the OCD side thus the chase for the sub-MOA capabilities. Have done quite a bit on the precision reloading side and actually shot a 10 round sub-MOA group with this rifle but it was never consistent.

As for the “stringing”, I am still kicking myself for not doing what I set out to do today. Originally, I was going to chrono all the rounds combined together with a video camera placed close to the target so that I could associate possible fliers with “outsider” MVs, but when I got to the range, there were two other shooters there which made this complicated arrangement difficult, still I may go back and do it with another 10 rounder.

The rifle does have a free-floating barrel.

As for the scope, this is actually the second scope with similar results and unfortunately don't have a third scope...