I have put together an AR with the following components.
Aero upper.
18" Faxon Gunner barrel rifle length gas system, 1 in 8 twist.
Brownells Chrome-Plated BCG
Faxon low profile gas block
Colt smooth free float match handguard. Older unused one gifted to me.
ACOG 4x32 on top.
No-frills DPMS lower.
All screws are tight and checked three times.

I have shot about 300 Barnaul 55 gr and 200 rounds Fiocchi 55 gr over five trips to the range and am not impressed by accuracy or consistency. I have shot this rifle calmly off a bench or prone, no mag dumps.  I expected the barrel to string a bit as it got warmed up, but not 5- 6 “ and shots rising at 100 meters with Fiocchi.
The thing that makes me question my build is that when I switch out the upper with an Aero 16" mid length, FSB and carry handle sights, I get 6 - 7” groups with the same lower. Since the frontpost take up more space than that I'm ok with that, for now.

When I shoot my 308 Howa at 100 meters I have five shots within an inch. I am no expert but know my fundamentals.

I have several stripped uppers, and my current theory is that the upper to barrel fit might be the problem.

Please advise.

I wonder if you shoot federal gold medal in your howa?

Try some federal gold medal in the ar.  Honestly ammunition is most likely problem.  

After that I'd start with barrel torque and a visual on the muzzle device.

I have a gunner barrel in 6.5 that shot lousy with all the factory ammo I tried including premium target loads.  When I say lousy I’m talking 2 moa or just a bit over.  Was really disappointed in it until I worked up hand loads using Berger bullets and Lapua brass.  Now it shoots .5 to .75 moa depending on how well I’m shooting on whatever particular day.

What is your trigger?  What's the trigger in the .308?

You're comparing apples to oranges with a 308 bolt gun (presumably with more magnification than 4x and possibly better ammo) to to an ar with standard 55gr ball ammo and 4x.  5-6" is a little bigger group but honestly i think 3-5" is typical with standard ball ammo and 4x magnification.  Depending on your trigger, etc. i'd start with dropping the comparison to the howa and try some high grain, match ammo on the AR then report back.  

Let someone else shoot a few 5 shot groups and see how they shoot; that will determine whether its the gun or the shooter.

To add to this just about any quality bolt gun with a decent scope is going to print a good group at 100 yards from the bench.

Sounds like a lead sled might be a good thing to have to test like this.

I'd bet handloading would cut your groups at least in half.  You could also try shooting @ 50 yards so you can get better target acquisition with that reticle, as well as the irons.  You can then just double your group measurement to equte to 100 yards.  What type of target are you shooting?

First thing I would try is better ammo with heavier bullets.

From personal experience, 4X magnification @ 100 yards with bulk 55g gives you about that kind of group.

4X "mid tier" LVPO
16" DD CL barrel.
Pretty lousy

Attached File


Same gun with the cheapest 12X scope Vortex makes
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55 grain is not optimal for a 1:8 twist. Try 62-77 grain match ammo and I bet you'll see an improvement.

ETA: I agree with cschelk2, let someone else shoot it before you start experimenting with ammo.

Use good ammo for benchmarks.



I know you said the screws are tight, but is that forend the one with the integrated barrel nut? How did you torque it?

My 55 grain handloads will shoot sub-moa in all of my 5.56 guns.  They all have 1:7 twist barrels.  Twist is fine.  There are many other factors that have more to say than twist.

Thanks for taking the time to answer.
@raymondj441 I shot Norma match ammo in the Howa. So sure, but the Fiocchi is not Barnaul…  
@backbencher. The howa has a Timney trigger and the AR is stock. So sure, that might play a part. But I’m usually pretty ok with mill/stock triggers on other firearms. I shoot a better than this with issue G3 and 416 rifles.
@cschelk2 I know I am, but I can’t help feeling that the AR should shoot better.
@s4s4u Shooting at 50 yards sounds like a good idea. I’ll try that next time I’m at the range. I’ve mostly shooting Norwegian army silhouettes with single white patches to give a clear point to aim at. Not really usable at 100 and open sights, but helpful for when using optics.
@Exorpmtech I’ll try higher magnification.
@ Danger_Close Relieved to hear that I should not expect stinging at it heats up.  
@ JohnSmith6073 and @ Danger_Close Forend with integrated barrel nut indeed. Torqued to spec. But will check.

It is my first build. I will start by rechecking all nuts and bolts and then try heavier bullets / better ammo.
Then I’ll use different optics and letting a friend shoot it. I can do it all in one sitting.

You have all been very helpful. I appreciate this a lot.

Ammo.

Trigger. GI type triggers are usually better controlled with a high/firm grip and using the 2nd/middle pad of the finger. Don't "stage" it; pull through the creep.

Force vectors - how you're holding it. I suspect light presure into shoulder or too much up-pressure on the front.

Target. If the ACOG is daylight illuminated, try a 6 MOA/2 Mil solid black circle.

@Tedspread

I have shot about 300 Barnaul 55 gr and 200 rounds Fiocchi 55 gr over five trips to the range and am not impressed by accuracy or consistency. I have shot this rifle calmly off a bench or prone, no mag dumps.  I expected the barrel to string a bit as it got warmed up, but not 5- 6 “ and shots rising at 100 meters with Fiocchi.
The thing that makes me question my build is that when I switch out the upper with an Aero 16" mid length, FSB and carry handle sights, I get 6 - 7” groups with the same lower. Since the frontpost take up more space than that I'm ok with that, for now.

Are you saying you can see the POI will rise as the barrel heats up by 5-6" at 100 yds?  

Assuming you and the ammo are not at fault, having the upper receiver face not true could be a suspect. I'm lapping every build now because of an experience with a Model 1 upper I bought yeas ago. It was stringing rounds to the side and when I finally tore it down, found the face of the receiver was lower on one side than the other.

@Blowout Hm, "upper receiver face not true". Hadn't thought about that.

I think I'll break the rifle down and rebuild, and check every thing.

Ball ammo tends to be inaccurate.

I've found the Fed American Eagle 50gr ballistic tip ammo shoots tiny groups. Used to be able to get it pretty cheap at times also.

I don't think Barnaul or Fiocchi 55s will shoot better than you have, even with a better telescope and trigger.

The recommendations for ammunition loaded with precision bullets (Federal, RUAG, MEN, Norma, Lapua, etc.) will get you better results, faster.

You obviously have experience with G3 and HK416, so the transition should be easy.

Just one extra thought. I put together an upper using a Faxon "Match Series" gunner profile 16" barrel. When I took it to the range it was not shooting well at all. On a checnce, before I went back to the range again, I took off the muzzle device. 1" groups after that. Try it first, it the easiest.

YMMV

My goodness yes.  Bullet weight is not the issue.  I shoot 52 grain Berger Flat Base Target bullets (match grade handloads in Lapua Match cases, Fed GM primers) from a match grade 16" barrel at 100 and 200 yard bench.  Groups are sub 1/2 MOA.

OP needs better ammo, but not heavier bullets.  At 100-200 yards with 1:8 flat base 52-53 match bullets are lasers.  Good boat tails like Sierra SMK are close.  Longer, heavier bullets are for longer range shooting.

At 100 yard bench, ammo quality not bullet weight is what matters with 1:8 or 1:7 twist barrels.

Good tip.  I’ve been burned with that before.

I always test a new build starting with a bare muzzle, followed by either an A1 as a combo thread protector/FH or a purpose-built suppressor ready 3-prong flash hider.   Lots of brakes are fine, but a few open up groups.  Lots of brakes with comp ports push the muzzle down off target as bad or worse than naked muzzle rise in the opposite direction.

Update of a kind.

I haven't had a chance to work on the problematic upper yet but shot a match with the other 16" iron sights upper. (Aero mid length SKU APAR505631) I regularly hit 18" gongs at 200 meters with the same ammo so I'm not clearing the ammo, but leaning towards something with the Faxon barrel'd upper. I hope to have chance to work on it in a few weeks time.

New barrels need some break-in and/or this barrel may not "like" the ammo. I once had an AR with a 16inch govt profile barrel that would shoot 3-4 inch groups using standard Federal 55 gr. Switched to Hornady American Gunner 55gr and group size was cut in half.
Of course good luck finding American Gunner ammo right now....

I would back up. Clean the barrel thoroughly. Then try a quality ammo like Federal match grade etc. Then we can rule that huge gap out. Fiochii and Barnaul are not know for their accuracy. Even though the Hornady is good the Gunner is still just plinking grade.