[wdphillips]

I just sold a Bushmaster A1 Style 20” HB complete upper. The gentleman called me saying that the upper on his lower (which he had recently purchased) was inaccurate (5-7” groups at 50yds) with all kinds of ammo factory and reloads. The conversation was around there might be something wrong with the upper. The upper has had very few rounds through it, there is no physical problems (bulges, etc). However this is a very stout (heavy) upper. Since I never had a problem with the upper on my Bushmaster lower. I thought I would ask the experts.

What can make an AR-15 inaccurate?

I did notice that when mating the upper with his lower was very light and the take down pins were quite a bit lighter than I was used to. I do not believe the lower had ever been used and was one of the “new”, unknown brand, lower cost versions that have been permeating the market since the shortage.

I really did not think much of it at the time. Is it possible that the heavy upper is driving instability in the lower?

[Tarant]

Does the rifle group the same when fired by other people?
My money is on the operator.

Is it a carbon/plastic lower?

[LA_357SIG]

In order of most likelihood:
1. the shooter.
2. ammo
3. trigger
4. uneven barrel crown
5. loose barrel nut
6. barrel harmonics

[PVolk]

I'd have him work in some match grade ammo to rule out his ammo as the culprit.

I've heard that tightening the barrel too tight could cause accuracey issues, but I don't think it would be as severe as 10-14 MOA.

[TedG]

What kind of groups did you get when you owned it?

[PVolk]

Originally Posted by LA_357SIG

5. loose barrel nut

It's it pretty much impossible for a barrel nut to come loose due to the gas tube preventing it from spinning?

[LA_357SIG]

Originally Posted by PVolk

It's it pretty much impossible for a barrel nut to come loose due to the gas tube preventing it from spinning?

It is very possible to not have the barrel nut properly torqued at the factory, resulting in deplorable accuracy.

[WoodenPlank]

Originally Posted by Tarant

Does the rifle group the same when fired by other people?
My money is on the operator.

Is it a carbon/plastic lower?

Definitely have him get a friend to shoot it. Best money is on operator.

[DJ Niner]

Originally Posted by LA_357SIG

In order of most likelihood:
1. the shooter.
2. ammo
3. trigger
4. uneven barrel crown
5. loose barrel nut
6. barrel harmonics

Good list, but I wonder what type of sighting system he is using. If an optic was involved, I'd put "Potential optics problem, including loose mount(s)" between numbers 3 and 4 on your list. I might even be convinced to jack it up to between #2 and #3.

For it to be attributed to problems number 2 or 4 on the original list, I would expect to see oblong or profiled bullet holes on target to cause groups like that at 50 yards.


.

[BenjiEDF]

Originally Posted by LA_357SIG

In order of most likelihood:
1. the shooter.
2. ammo
3. trigger
4. uneven barrel crown
5. loose barrel nut
6. barrel harmonics

Pretty good list. I'm betting it's mostly 1 and 3. 4 is easy to inspect. 5 and 6 not likely.

Does the shooter know how to use A1 sights? I bet the trigger on that lower sucks too.

[wdphillips]

Thanks for all the tips guys. I am going to talk with him again this morning to try and get more information per all of your questions.

Although I did not shoot the upper that much, 20+ rounds, I did not ring it out for accuracy. The upper was a varmint rifle project that did not get off the ground.

I checked my load data and I did chrono it against my Colt, DPMS, Bushmaster, and BCM for my .223 load build up. It was right there next to my BCM for velocity.

I really feel quite bad that I sold him an upper that he is having problems with. That was not the intent.

I did ask him yesterday to switch lowers if he could. I do not know what his new lower was built from but it was very light.

I do remember talking with a gunsmith a while back on accurizing an AR. There was a lot of discussion around beading the lower to the upper at the rear pin. I cannot help but think the lower is a contributing factor.

[Big Bird]

The mating of the lower and upper receivers has almost no affect on accuracy.

Here are some things that might affect accuracy. Loose flash hider. Loose Front Sight Base, poorly fit bolt or lack of proper contact on the locking lugs in the barrel extension. While its mostly true the barrel nut can come loose as the gas tube keeps it in place...there is the possibility it wasn't torqued properly at the factory and is in fact loose.

[Bren]

The shooter.

I was selling a match upper on GT that I have shot 100 yd groups with all shots touching, but I decided not to sell when newbs here started asking for accuracy guarantees. Most people, including people who have shot for years, can't shoot.

Those who can't shoot and don't know much about it always blame equipment. They think a magic sight change or grip change or polish job will overcome their lack of proper fundamentals.


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[bullittmcqueen]

There are some good replies here; the answer is more than likely going to be Shooter, Ammo, or optic/mount. If he threw a Truglo optic on there in a UTG mount then there you go. I've seen really good shooters scratch their heads all day because they couldnt figure out why their $25 red dot wouldnt shoot better than 10 MOA......SIGH.

You need some more info from this guy. I wouldn't hang my head if I were you just yet. Chances are the upper is just fine and you did nothing to feel bad about.

[crazyasian1]

7. Buyer's remorse

[TangoFoxtrot]

Originally Posted by LA_357SIG

In order of most likelihood:
1. the shooter.
2. ammo
3. trigger
4. uneven barrel crown
5. loose barrel nut
6. barrel harmonics

Good response!

[Glockengraver]

There are some good responses here....I think first you need to be able to make sure it is not the shooter or optic (if there is a optic) causing the issue.

I remember years ago taking my brother out with my AR-30 in 300 win mag. he was not very impressed with it as it was shooting 2 to 4 inch groups.....I sat down behind it, thinking WTH, and proceeded to shoot 1/2" groups with the same ammo......

[M&P15T]

I think you're being snookered OP.

Do you run a gun store or something? I'm betting it's a combo of buyer's remorse, and a terrible shooter.

[wdphillips]

No I do not own a gun store. This was just another average gun guy to another average gun guy. Both members of Rocky Mountain Gun Owners.

BTW there is no optics involved, just standard AR15, A1 open sights.

I did give the gentleman a pointer to this Thread. Hopefully he will find something that will help.

I should add that the buyer never asked for his money back. I believe he was just disappointed in the way it shot and I was disappointed that he was disappointed!

I thought if I could help find a reason for the large groups it would help him. You guys have been extremely helpful. I hope he pops in and reads the thread.

[CAcop]

Originally Posted by PVolk

It's it pretty much impossible for a barrel nut to come loose due to the gas tube preventing it from spinning?

We have Colt 6920s at work. One ended up with loose barrel. It was all over the place.

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[eccho]

Originally Posted by wdphillips

Somebody doesn't know how to aim.

Fixed.

[B.Reid]

Probably a heavy trigger and a poor shooter. If it was accurate on your upper it is operator error on his part.

[wdphillips]

Originally Posted by eccho

Fixed.

Not that I know of.

[NEOH212]

My first thoughts are to try a different shooter and then different ammo. If none of those two things cure the problem, than look at the mechanical side and start troubleshooting from there.

My bet is the shooter can't shoot.

[jakebrake]

Originally Posted by LA_357SIG

In order of most likelihood:
1. the shooter.
2. ammo
3. trigger
4. uneven barrel crown
5. loose barrel nut
6. barrel harmonics

leaning heavily on those first 3.