Barrel Indexing/clocking question

[bobafett]

1st, Yes it's a Bushmaster...

I put together an AR pistol. I used an 11.5 barrel, in the chance I wouldn't like a pistol I could pin a 5" flash hider and make it a legal carbine.

This is the same barrel I fudged up a couple teeth on the barrel nut.

I went to break it down so I could replace the barrel nut before I have the flash hider pinned. Just removing the flash hider and the barrel clocked inside the receiver a slight bit.

I had another Bushmaster do this, so I used it as an excuse to install a YHM free float rail and it never clocked again.

I really don't want to put a free float rail on this one, what do I do to properly keep the barrel from clocking when I install the new barrel nut?

Where can I get shims?

[Iraqgunz]

What is clocking? I am confused? Are you say that the barrel rotated a little? If so, there is something wrong. The barrel extension has a barrel pin and the upper receiver has a barrel alignment notch on it and it shouldn't move unless the hole is messed up.

If there is any movement or play it should be very minimal.


1st, Yes it's a Bushmaster...

I put together an AR pistol. I used an 11.5 barrel, in the chance I wouldn't like a pistol I could pin a 5" flash hider and make it a legal carbine.

This is the same barrel I fudged up a couple teeth on the barrel nut.

I went to break it down so I could replace the barrel nut before I have the flash hider pinned. Just removing the flash hider and the barrel clocked inside the receiver a slight bit.

I had another Bushmaster do this, so I used it as an excuse to install a YHM free float rail and it never clocked again.

I really don't want to put a free float rail on this one, what do I do to properly keep the barrel from clocking when I install the new barrel nut?

Where can I get shims?

[bobafett]

Yes there is room for the pin to move slightly side to side.

I can measure the pin and the cut out if it'll help tell which is out of spec.

[Iraqgunz]

I don't know what to say to be honest. Even when I have worked on Bushies in the past I didn't have an issue with any real slop. You could try another upper.


Yes there is room for the pin to move slightly side to side.

I can measure the pin and the cut out if it'll help tell which is out of spec.

[bobafett]

The pin is .126+/- and the cut out is .128+/-

I can only get the tip of the micrometer on the pin

[Col_Crocs]

How does the barrel movement on this upper compare to your previous upper?
Hard to say without personally handling it and Im not sure the numbers you provided are within spec tolerances but sounds to me like your barrel nut wasnt torqued to spec to begin with, hence, the movement.
If it is within normal tolerances and neither part is damaged or out of spec, torquing your new barrel nut to spec should eliminate said movement.
Do go over each part carefully though. Check for damage, compare the numbers you took to known good parts if you have any and try a new receiver like IG suggested and see how the movement compares, if it all. Keep us posted.

[bkb0000]

two thousandths isn't going to make a difference. torque er down.

[bobafett]

How does the barrel movement on this upper compare to your previous upper?
Hard to say without personally handling it and Im not sure the numbers you provided are within spec tolerances but sounds to me like your barrel nut wasnt torqued to spec to begin with, hence, the movement.
If it is within normal tolerances and neither part is damaged or out of spec, torquing your new barrel nut to spec should eliminate said movement.
Do go over each part carefully though. Check for damage, compare the numbers you took to known good parts if you have any and try a new receiver like IG suggested and see how the movement compares, if it all. Keep us posted.

This was a new build, Bushmaster barrel and PalmettoStateArmoury upper (Keyhole Forge Marking) I didn't have any other barrel or upper combo to try.


two thousandths isn't going to make a difference. torque er down.

That's all, just slight movement because I didn't get the barrel nut tight enough. Glad that doesn't seem excessive, I'll make sure I get this barrel nut locked down good this time.

[Surf]

Not sure how tight you had the barrel nut, but it should fall somewhere between 30-80ftlbs.

[bkb0000]

and make sure you give the barrel extension rib some anti-seize when you coat the threads. helps keep the nut from wanting to tug the barrel over with it.