Question about my AR-15's accuracy

Everything solid? Barrel tight? Front sight tight?
My first AR was a kit built commando shorty, and I found after I shot it the first time that the barrel nut and front sight were both slightly loose...after they were tightened up, it shot very tight groups at 100yds.

I have a bushmaster and it was the most accurate out of the box gun I have ever owned. When I have problems with sighting a gun I usually have my brother shoot it also and see what it is doing for him. sometimes it is all me and sometimes it is the gun.

How were you shooting the rifle? prone, with or without a sling? from a bench?
any kind of support?

I have seen several "floating" standard rear sights, its at least worth checking out if you were using iron sights.

If the sights and barrel check out ok and you find nothing loose or broken the next thing I would try is different ammunition.

My bet is that the sights are the issue. If you are getting 20" groups then its almost always the optic or sights that arent working right. Do you know the barrel twist on your rifle? There aren't many makers that make a 1-12 inch twist, but if you have one it won't work well with 62 grain bullets.

Oh yeah, dont buy from CTD.

I very much doubt that the ammunition has much to do with this. Most bushmaster rifles have a 1/9 twist, but some have a 1/7 twist. Either twist rate should work fine with 62gr. Brown Bear ammo.

But hey, just for the hell of it, get a box of PMC and test it.

Alright, first I'd check the sights to see if they're tight, like others have said here. Secondly I'd try to see if your barrel nut is loose. This accuracy usually happens when the barrel nut is loose. If that is the case, you can either repair it yourself (which requires a few expensive tools and a little bit of mechanical expertise. Do you have an adjustable torque-wrench, vice, AR-15 armorer's wrench and upper receiver vice block?), or you could send it back to Bushmaster to get the repairs done.

Just send it to bushmaster. You would have already figured out if your barrel was loose if you had those tools.

20" groups at 100 yards says something is definitely wrong. Good ammo should give you 2" at 100 yards at least, Russian ammo maybe two or three times that. But 20" suggests a mechanical problem or a bad barrel crown or something.

You could try contacting the factory, but I'd try better ammo first.

Possibly the hider is torqued down too hard and has "pinched" the muzzle... seen it on factory FN A4's...

Don't mean to be negative, but how well do you shoot other rifles? Might not be a hardware issue..

Try better ammo--Winchester, Federal, Remington, PMC 55gr fmj.

If no improvement, call Bushmaster.

I had a Colt AR-15A2 20" 1:7 HBAR that produced desk calendar size groups (no exaggeration) at 100 yards with LC 62gr M855 ammunition. However it shot great groups with 55gr M193 - headshots on IPSC cardboard targets (6x6" target area) at 200 yds with iron sights were a piece of cake.

Off a bench?? Is your magazine off the bench top or touching? My son had issues with his until he started using smaller mags that didn't touch the bench top

I'm gonna call bushmaster tomorrow and see what they think.

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That's a good idea. It stinks to have issues with your new AR. Good Luck

Cliff Notes - check the bore for burrs

Walley -

I had an issue similar, but not exactly the same as yours. I was shooting a brand new upper, from a well known maker, who guarantees 1 MOA, "right out of the box". My problem corrected itself in 10 shots. But, the first six, had me very mad:







Yes, they were key-holing. You can see in the last picture, the skidmark left when the bullet tumbled across the grass, about 25 yards from the muzzle, and actually bounced up into the target.

I got on the phone after the first three shot string, and the CS rep asked me to email him the photos. I did just that, and while my buddy and I were waiting, we figured we fire another 6-7, since we'd probably be sending an upper that I'd waited a very long time for, back to the company. It straightened itself out - in the next 6-7 shots, they began to group back together, where they were supposed to be. Our best guess, is that some sort of machining burr or debris was still in the barrel, and the first 6 shots either wore it down, or knocked it out.

Check your bore, with a good light. Give it a thorough cleaning. If you shoot again, and still no improvement, I'd be on the line to Bushmaster HQ. I'd also consider this an anomaly - Bushmaster has a pretty damn good reputation for a reason. Just my .02 cents. Good luck.

-tc

So how can I tell if the barrel nut is loose?

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Grab the front sight base and the upper receiver. Try to twist them relative to each other. Any motion means your barrel (and barrel nut) is loose. BSW

Something is definitely wrong with the rifle. I have had a few gripes about Bushmasters but accuracy was never one of them. I have owned 2 Bushmasters and carry one for work. They are accurate rifles.