AR upper assembly question

[Bat Rastard]

I have an AR that doesn't shoot as well as I think it should. It is made of good parts, so it has to be the assembler, (me) right?

The junction where the handguard meets the receiver is flush. Should I releive the handguard to provide some clearance there? .030 is where I think I will start. Or is this a bad idea?
I am soon to tear it down to lap the receiver. This would be the time to do it.
Any advice would be appreciated.

Thanks , Bat

 

[Eagle Six]

I wouldn't Bat. What do you expect to gain?

 

[Bat Rastard]

I want to gain half an inch or so reduction in group size.

My thinking is:

Parts are moving and flexing during the firing process.

With the flush fit, it impedes and affects the flex. Possibly not the same flex every time.

Therefore, if I releive it, it will flex and return in a more consistent manner.

Perhaps I am over thinking this, but it seems logical to me. I am fairly handy with a grinder and a stone. With a dab of black paint, I think it will be adequately pretty.

 

[jelenko]

From my experience it would be worth a try.

An AR's accuracy comes principally from the barrel.
When you put the barrel in, how tight was the fit?
Who provided the barrel?
Whose upper?

Are you comfortable that you can shoot the group size you're looking for assuming the rifle that would shoot much smaller? I.e., the rifle would not hold you back at all.

 

[LVLAaron]

I don’t think that would matter. The hand guard is tight to the upper regardless.

 

[LVLAaron]

lap and bed it.

Check the gas system

Make sure the gas rings aren’t too tight or too loose.

 

[LVLAaron]

Any chance you have a set of gauge pins in the one inch range?

 

[Bat Rastard]

This project started with two Armalite NM rifles 30 years ago. In 2000 we rebarreled them with Krieger barrels, then stopped stopped shooting them.
We are getting back into shooting them but not shooting HighPower. I have been migrating parts into flat top uppers that are more appropriate for what we are doing now.
I know one of the new uppers is Aero Precision, and I think the other one is too.
I just received a White Oak handguard and it has clearance that the one in the picture doesn't. Not sure what brand it is, it has an M on it.
I haven't bought the cheapest parts, nor the most expensive.
I can shoot fairly small with other rifles, so I think I have an equipment issue.
I am trying to get from 1.25"ish to .75"ish.
I don't have access to gage pins that large but the Wheeler lapping tool was a snug fit.
I am using a wedge to eliminate upper/lower fitment.

 

[Bat Rastard]

Gas block is a new adjustable with a new tube.
The barrels and bolts have stayed together in matched sets.

 

[js2013]

It could be a zillion things but I’d add clearance between the hand guard and the upper especially if your still shooting from a sling. No guarantees but it won’t hurt anything.

 

[Bat Rastard]

It could be a zillion things but I’d add clearance between the hand guard and the upper especially if your still shooting from a sling. No guarantees but it won’t hurt anything.

We have given up on slings and open sights. I will give it a grind and keep looking at a zillion minus one other things.

 

[Coyotefurharvester]

I would be concerned with the barrel nut/ receiver clearance and proper barrel nut torque. Work out from there.

 

[jelenko]

Check the gas system

Make sure the gas rings aren’t too tight or too loose

Have you found either of these to affect accuracy? What in the gas system?
Thanks

 

[LVLAaron]

Have you found either of these to affect accuracy? What in the gas system?
Thanks

Gas tube alignment. Gas key fitment, do the gas rings run smooth? if they're tight and dirty, they're inconsistent, and are you getting consistent recoil and recoil management (you, not the gun) - There's a bunch of things banging around when an AR cycles... All those need to be the same every time.... Purely anecdotal, but my AR's that are way over gassed are the most accurate. I'm sure there's something to that, but I'm not going to test it

 

[jelenko]

getting consistent recoil and recoil management

Ah!
If you're shooting from a sling position, does that help/tend to improve overall consistency of recoil management?
Thanks

 

[10XSHOOTER]

If your handguard is free floating and not touching the barrel. Look elsewhere!
You lapped the front of the receiver? Did you use blue lock tight on the barrel extention?
Torqued 30-40 and finally 50 ftlbs. Is your gas tube centered in the upper? Not pushing to one side or the other? Have you played with the adjustable gas block? close it. open with one shot at a time until the rifle fully functions. then add 2 more clicks.
Finally what twist and bullets are you shooting? Do the bullets match the twist?

 

[Rocketvapor]

Worried about handguard flexing differently with different loading due to contact with upper?
With a gap, would the handguard flex even more?
When you lap a little off the receiver the barrel moves back a teeny tiny bit.
I see a rest in your picture.

 

[dellet]

It’s never a bad idea to have a free floating handgaurd, actually float freely. But if you’re getting enough flex there to effect accuracy, the barrel nut is probably loose, or not making full contact with the barrel extension at the upper.

Is it possible to slide the guard forward, or does it thread onto the barrel nut?

If it threads on, back it off a turn and see it it makes a difference.

 

[Bat Rastard]

Thank you all.

I am going to lap the receiver and loc-tite the barrel extension.
I will report back after testing.

 

[Knotwild]

The first thing I would try before any major modifications is making sure the rifle recoils freely in that rest I see in the picture. Also on the back bag. Especially if your group is stringing vertically. I had an AR shoot ok for me, but the hand guard was not recoiling in the rest consistently. Probably due to the grippy design of most hand guards. Plus, most of the weight in an AR, especially with a long and heavy barrel, makes a lot of friction on that front rest. I accomplished this by slitting a paper tube and putting it between the bag and the rifle and making sure no sling swivels were hitting the rest or back bag. If I shot AR's like that a lot, I would buy a bag rider.

I also use this AccuShim instead of those rubber plugs. It is much better.

If you weren't using the rest I see in the picture, forget everything I just wrote.