AR-15 not grouping consistently

I think it's time you took that beautiful rig to a good
gunsmith and have him take a look at it.

Zeke

Assuming everything is tight and secure, I would first try shooting with iron sights to make sure it's not the scope, or change the glass. If it still shoots off, try using copper remover in the bore. Next try 55 grain loads. After that, I would send the barrel/upper back if possible.

Have you tried a 68/69 Match Bullet, 55 will be not near the results ?
What Twist is your AR Barrel ?
What load are you using, Factory or reloads ?
Barman54
Out

Two things come to mind. Scope/mount issue, I had a high end quick release mount and a Nightforce scope. I ended up finding out I had a defective mount.

Barrel? Good quality match? Barrel twist?

It could be several issues,but I have a similar issue with an AR that I built last year. I have a 18" Seekins Precision barrel on it,and it just will not shoot any bullet/powder combination consistently.
I've tried 15 different bullets from 55 grain to 77 grain with 13 different powders loaded from minimum to maximum loads. Nothing works well!
Today was my last battle with it,the barrel is going into the trash can. I've built quite a few AR's over the years from cheap plinkers to high end target rifles,and this is the worst shooting AR that I've ever owned.

Sometimes High quality parts just don't work like they should!

I'd try some light loads, like 50-55 grain to rule out a bullet weight preference. Next up I'd look at the optics and mount. I had a scope once that drove me nuts, on a 7.62X39 upper, finally pinpointed the scope, sent it in, got a new one, rifle shoots great now.

With a bull barrel, I'm assuming no muzzle device that could affect it. Crown look good?

I'd look at the optic or mount. I've never had an AR that grouped that poorly, not even my 14.5" ultralight with a $95 barrel that I turned several ounces off of on my lathe. Even that one is around 2 MOA at 100 with ball ammo. My 22" Wilson bull barrel with a 5.56 chamber is sub-MOA at 100 with just about everything.

I had a similair problem a few weeks ago. Repeated cleanings with a copper cleaning bore cleaner fixed it. You could have other issues but I would start there. Rapidfire, high volume and high velocity makes copper fouling.

Rings? Haven't used those on an AR in years.

Never going back to anything else:
http://www.larue.com/larue-tactical-spr-m4-scope-mount-qd-lt-104


Make sure push the mount all the way forward against the rails edges when tightening the QD's down.

I have built*

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First build? Take rifle to gunsmith that specializes in match grade AR's

Is the scope base attached to the upper only? Or is the front ring mounted on the handguard?

Has to be scope/mount related...unless something really screwy with the barrel.

I had a similar problem with a Sako .243. I messed with it for 15 YEARS, trying off and on to find a good load. Finally, I removed all the copper deposits from the barrel and then lapped it with J-B Compound. Then I lapped it more with J-B Bore Brite. That barrel looked like a mirror inside. That brought the groups down from 1.5" or 2" to .75". Some barrels are just weird. If it's not your scope/mount, it's the barrel....

Try changing the BCG.

whoa, 3-5 inch groups at 100 yards with a match load in a 24" barrel?
what is the twist?

I think you have a bad barrel. That rig should shoot sub MOA with match ammo.

If you are 1:8 or 1:7, check out the ASYM precision 77r load. It is VERY VERY accurate factory ammo. Try that instead of handloads first.

Is this a 1:8 twist? If it is I would work with 69 SMKs.
How well do you normally shoot?
3.5 lbs is a little heavy for a target rifle. Any chance you are pulling your shots?
24" id s lot of barrel. Not saying that's the problem but why did you choose that. You might want to consider taking of 4" and re-crowning.

I had a problem with a 24" 1/8 twist SS bull barrel. Tried just about anything i could think of. Bullets from 55 to 79 or 80 gr. Several powders and charges from min to max in .1 gr steps. I lapped the crown twice and no change. I was going to cut it up in 1' segments but decided to try a 1/4" rotary tapered file in my drill. Moved it in slowly and it grabbed on the righr side and a few chips came out. Well that's the end of that, but I thought I'd try it again with 77 gr bullets. Groups <1" great. That was fooling around with it for 2 years.

RainDodger said:

Finally, I removed all the copper deposits from the barrel and then lapped it with J-B Compound. Then I lapped it more with J-B Bore Brite.

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This might belong to gunsmithing section, but hand lapping a suspect barrel is by far the best way to make sure it's what it's supposed to be. Once you get familiar with the technique, it only takes one evening to do it properly, avoiding the pitfalls of ruining the throat or muzzle/crowning in the process. The worst one so far was a 16" AR bull barrel I spent a sizable amount of money on. It was supposedly hand-finished state of the art item from a very reputable manufacturer. In practise it wouldn't group at under 2½" at 100yd with any ammo. Eventually I checked it with borescope and hand lapped it. The result? 0.4MOA cloverleaf with the first five shots of factory ammo I tried. A more than sixfold instant improvement and with handloads it shoots one ragged hole now.

It never ceases to amaze me how many times even a high-end barrel is less than perfect and why so many people are so afraid to use abrasive compounds on their barrels to correct possible problems. Fire lapping has gained some popularity during last few years but casting a lead slug and doing it properly is amazingly rare. There's no magic to it, just patience and following known good principles throughout the process.

I was going to make hq's suggestion. Slug the bore and see what it feels like going down. This and the end diameter of the slug can tell you a lot about whats going on. Then lap it. You should also make a chamber casting and see whats going on there cerosafe is the stuff i think its called.. Thats what i would do if nothing else is obviously wrong. Definately mount the scope (and rings you are using) on another rifle known to shoot well and make sure thats not the problem.