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bad accuracy with new AR 15 barrel


mark75101

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About a month ago I put together another upper using a Rainier Arms Select 16" 1/8 mid length. I've tried 52, 55, 62, 68 and 69 grain ammo and it seems to shoot about 3 1/2"-4" at 100 yards. I tried 3 scopes and two shooters, got frustrated and sent the barrel back for replacement. The replacement is just as bad. I can put my 16" RRA upper on the lower and at least cut the group size in half.

Is there something I missed in the assembly? I really don't want to believe its the barrel.

The only thing I can think of at this point is the upper itself. Its a flat top thats been in my safe so long I don't remember where I got it. Can the upper reciever itself make a difference?

The rest of the specs:

Giesselle Mk 4 rail, barrel nut torqued to 40 ft/lbs as per instructions.

MI low pro gas block (3 set screws)

A2 flash hider, althought I did try it without a flash hider just to take it out of the equation.

Tried two lowers, RRA with 2 stage NM trigger and Spikes with Fail Zero trigger.

Leopold 12X with fine target dor

TA31RCOM4 acog

2.5X10 Vortex.

Any ideas?

Thanks

Mark

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Three probabilities, provided you are using quality ammo:

1. Barrels not good.

2. Shooters not good.

3. Combination of upper receiver to barrel extension fit, barrel nut and torque level...not good.

There are other things that are possibilities...lightweight profile barrel with set screw gas block, muzzle device not concentric with bore, cutting bullet on feedramps that are improper,

I'd bet on #3 based on your description.

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Are you shooting factory ammo or reloads? What kind of pattern are you seeing at 100 yards? Random or stringing of shots?

Is there a chance the gas key is rubbing the gas tube?

Have you tried shooting the gun without the compensator installed?

When installing the barrel nut, did you torque and release, then repeat, and then torque a final time to align the gas tube? Are you comfortable torquing the barrel nut a bit more? If I remember correctly, MarkCO in another thread indicated he went as high as 80 ft-lbs on some uppers.

Is the gas block fixed in place with a set screw? If so, did you dimple the barrel for the set screw?

When you installed the gas block did you leave a slight gap between the barrel and the rear end of the block? (I position a credit card between the two before I tighten the gas block.)

These were all the things I covered when I had problems with a barrel last fall. Turned out its just a mediocre barrel.

Bill

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Ok. So, the lower has no effect on accuracy. You say that you have shot better groups with the ammo you have tried in the RRA upper, so this should indicate that your ammo is a known component. You have tried more then one shooter and scope, so this is all quite good in getting down to the heart of the issue. There is the possibility that you have some kind of gas tube binding or misalignment going on. This would likely contribute to SOME of the issue. I would however check and make sure that your gas block has plenty of clearance inside of your hand guard. I would also check and see how easy it is to move the barrel inside the hand guard and in general make sure everything is tight. If there is gross movement, you would see and or feel it. I highly doubt that the barrel is the issue, especially if you are on your second one.

I suspect that something is not right with hand guard installation or your upper is out of spec.

You are not bridging the upper and rail with your scope / mount are you? the scope(s) should only be on the receiver.

Knock on wood I have not had an issue with an AR build to date.

Pictures please...

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How was the fit of the barrel extension in the upper? I've seen some billet uppers that were disgustingly oversize in the bore. That can not have a good impact on accuracy.

Seemed pretty tight

That's a subjective term. Did it need a rubber mallet to fit, did the muzzle wobble back and forth prior to the nut being tightened?

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Are you shooting factory ammo or reloads? What kind of pattern are you seeing at 100 yards? Random or stringing of shots?

Is there a chance the gas key is rubbing the gas tube?

Have you tried shooting the gun without the compensator installed?

When installing the barrel nut, did you torque and release, then repeat, and then torque a final time to align the gas tube? Are you comfortable torquing the barrel nut a bit more? If I remember correctly, MarkCO in another thread indicated he went as high as 80 ft-lbs on some uppers.

Is the gas block fixed in place with a set screw? If so, did you dimple the barrel for the set screw?

When you installed the gas block did you leave a slight gap between the barrel and the rear end of the block? (I position a credit card between the two before I tighten the gas block.)

These were all the things I covered when I had problems with a barrel last fall. Turned out its just a mediocre barrel.

Bill

1. Both factory and reload. Random groups at 100

2. Slight rubbing on the gas tube with the fail zero bolt. The RRA seems smooth as silk, its a old BCG with alot of rounds through it though.

3. Yes. No change.

4. Torque, release, no repeat. Maybe thats it? The first barrel I torqued to 40, after seeing bad accuracy I pulled the forend and torqued to 45, no change. Haven't tried re-torqueing the second barrel though. If you think it might help I'd have no problem torqueing to a higher ft/lb.

5. Yes, 3 set screws. The barrel came with one dimple which did line up. I did not dimple the other two, just tightened till it hit the barrel and called it good for now.

6. Yes, probably not credit card thickness though. Just a slight gap because thats where it ended up with the factory dimple for set screw.

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Ok. So, the lower has no effect on accuracy. You say that you have shot better groups with the ammo you have tried in the RRA upper, so this should indicate that your ammo is a known component. You have tried more then one shooter and scope, so this is all quite good in getting down to the heart of the issue. There is the possibility that you have some kind of gas tube binding or misalignment going on. This would likely contribute to SOME of the issue. I would however check and make sure that your gas block has plenty of clearance inside of your hand guard. I would also check and see how easy it is to move the barrel inside the hand guard and in general make sure everything is tight. If there is gross movement, you would see and or feel it. I highly doubt that the barrel is the issue, especially if you are on your second one.

I suspect that something is not right with hand guard installation or your upper is out of spec.

You are not bridging the upper and rail with your scope / mount are you? the scope(s) should only be on the receiver.

Knock on wood I have not had an issue with an AR build to date.

Pictures please...

No bridging.

Scope mount for the leopold is not great lol but seems to work. Its the set up I use whenever I get a new rifle just for checking loads. The Acog has a LaRue mount and the Vortex has a ADM mount.

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How was the fit of the barrel extension in the upper? I've seen some billet uppers that were disgustingly oversize in the bore. That can not have a good impact on accuracy.

Seemed pretty tight

That's a subjective term. Did it need a rubber mallet to fit, did the muzzle wobble back and forth prior to the nut being tightened?

Yes I guess it is subjective. It did not seem loose but it slide right in. No mallet needed.

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Pull the HG off, then shoot a group. If still bad, torque nut up to 60 to 80 and shoot a group, still no HG and shoot a group. If still bad, pull the gas block off and shoot a group, still no handguard. This will narrow it down to just the barrel nut, barrel and receiver.

Yes, you can shoot an AR with no HG and no GB. Just make sure you are aware a hot plume of gas will be coming out of the gas port, and it will not cycle.

HGs and barrel nuts account for the vast majority of accuracy issues with otherwise good components.

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.

4. Torque, release, no repeat. Maybe thats it? The first barrel I torqued to 40, after seeing bad accuracy I pulled the forend and torqued to 45, no change. Haven't tried re-torqueing the second barrel though. If you think it might help I'd have no problem torqueing to a higher ft/lb.

I don't know if the 2nd torquing is required or not, just the way I've always done it.

Increasing the torque a bit won't hurt and if you're lucky might help.

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The "final where I want it" typically means lining up the gas tube hole on the barrel nut.

The reason to tighten and loosen 3 times is to break in the threads of the barrel nut to the upper receiver.

Grease the threads on the upper. Turn the barrel nut with the wrench till its snug and back it off.

When you tighten again, you will notice the barrel nut will turn a little further is you apply exactly the same torque.

Like mark, I used to tighten initially to ~40-45 using a torque wrench. I no longer bother. Just past tight is ~40-45.

After backing off the nut on the 3 go, tighten till the gas tube hole aligns. You will find that you are typically in the 60-85 range when you are done....

Mick

I always torque a minimum of 3 times to about 50, then the final where I want it.

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  • 3 weeks later...

Got a break in the weather and went back out.

Tried increasing torque, shooting without the rail/ shooting without the gas block and tried the barrel on another upper receiver. No change.

Also tried three more loads: Hornady super match 75 gr, a 77 gr handload a buddy had and a 60 grain sierra loaded with data 68. The 75 gr group was about 3 1/2" at 100, the 77 gr was 1 1/4" the 60 was just under 1 1/2".

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  • 4 weeks later...

Last idea that I have is that there might be an issue with the compensator that you are using on the rifle if you are testing with it on the rifle. There are claims that if a comp is on too tight it can effect the bore but im not 100% on that idea, there is still plenty of metal. Also, if there are imperfections in the comp I suppose it might effect things too. Pull the comp and try shooting a group.

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The torque loosen 3-4 times then torque to spec is needed to kinda seat the threads and make sure grease is used. Also you can try squaring/lapping the upper. I do that on all mine from the get go. I did a friends colt that just shot like crap and it was a big improvement. That's the tool I use and use valve lapping compound for the compound. http://www.brownells.com/gunsmith-tools-supplies/rifle-tools/receiver-tools/ar-15-m16-upper-receiver-lapping-tool-prod20220.aspx

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