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bigsky
December 04, 2016, 14:44
This is a question???
putting my latest build together and noticed I need to add a barrel shim...Why would you add a shim on the barrel extension which I would think would change the headspace instead of adding a shim behind the delta spring...

gunshooter
December 04, 2016, 15:16
Why do you need a shim?

To clock the conventional barrel nut to clock the gas tube channel at the correct torque? - I rely on selection of barrel nuts.

To clock a nut that is part of a free - float handguard assembly? - I never seize the threads and work them a bit to get that bit of more rotation until over torque is achieved or again rely on a selection of nuts from the same or compatible MFG. The key hole light weight handguards I got included shims so in that case I suppose one can use them, but I try not to.

I can't think of reason for shimming an extension to the barrel. That is a complete change of headspace, caveot, unless you are doing a 6.5 LBC or 6.5 Grendel and using a type I-II bolt and don't have corresponding type I-II barrel-headspace dimension. But I still would not shim that situation, just use correct spec bolt for type I or type II headspace.

:tinfoilhat:

CG&L
December 04, 2016, 16:56
Something isn't right

I think you mean 'add a shim to get the barrel nut to time'
You can't affect the headspace without doing something to the bolt or take the barrel extension loose from the barrel

There are several makers of Ar-15 receiver lapping tools
http://www.brownells.com/gunsmith-tools-supplies/rifle-tools/receiver-tools/ar-15-m16-upper-receiver-lapping-tool-prod20220.aspx

and Wheeler makes one

bigsky
December 04, 2016, 17:09
yep, thats what i mean. It was a brand new rifle, took it apart, there was no grease on the threads, when i put it back together WITH anti sieze the standard barrel nut, while torquing from 30 to 45 pounds rotated just past perfect alignment.
Yep, I worded it wrong, I need to "shim the barrel nut"...When I looked on the web, bison armory showed a barrel nut shim kit, then watched their video and they showed pulling the barrel, cutting one side of the shim so it spaces around the extension pin, didnt make sense.

Any ideas on getting barrel "nut shims" ??

fmj_shooter
December 04, 2016, 17:17
Bison sells them, Spikes sells them, many others.

Shim in front of the barrel flange (between barrel and nut). You can do it the bison way but it offers zero advantage, with some possible disadvantages.

bigsky
December 04, 2016, 17:42
looking online,,i see shims sold that are .001-.003 and then other shims are .032,,should i stack the thin shims or get the .032" shims ?

fmj_shooter
December 05, 2016, 12:21
looking online,,i see shims sold that are .001-.003 and then other shims are .032,,should i stack the thin shims or get the .032" shims ?

You want thin shims, the .032 will adjust by over 1/2 turn , too much.

jhend170
December 05, 2016, 14:44
30 ft/lbs was adequate if you got there and the gas tube was in the right place. For accuracy's sake less is more.

It's also an opportunity to true the upper and lap the face of it. If the face isn't perfect the pressure applied around the extension flange can be uneven and affect accuracy. All the BR guys do it, and I do it to every upper I build or ever have apart.

Cornpone
December 05, 2016, 14:52
My gawd man WTF ! I've assembled thousands of ARs and never needed shims. Never needed to remove the FSB to remove a barrel. This guy has to be some kind of commie troll or a complete retard:facepalm:

CG&L
December 05, 2016, 16:44
No, he's just trying to get the barrel nut timed with the gas tube

Bigsky

Check out the receiver lapping tool. It'll allow you to slowly take a little of the receiver face until the barrel nut will align with the gas tube.

bigsky
December 05, 2016, 16:51
cornpone, did you stick your muddy boot in your own mouth,,i took the fsb off to paint it. read the entire post so you dont look foolish. you were saying,,retard..

FriendBesto
December 05, 2016, 20:15
Another vote for a lapping tool. It is great for this very purpose.
I seem to have bad luck with barrel nut timing.
Out of the 10? or so I have done, not one receiver face has been square with bolt raceway.

FALonious
December 06, 2016, 06:52
There are several makers of Ar-15 receiver lapping tools
and Wheeler makes one

https://www.google.com/search?q=AR+lapping+tool&ie=utf-8&oe=utf-8

Wow...lots of them. Who knew? Never messed with one before.

MistWolf
December 06, 2016, 07:34
There is s torque range that tends to give best the best precision and sometimes shims are needed to achieve that torque. Nothing retarded about it at all

jhend170
December 06, 2016, 10:41
30 ft/lbs was adequate if you got there and the gas tube was in the right place. For accuracy's sake less is more.

It's also an opportunity to true the upper and lap the face of it. If the face isn't perfect the pressure applied around the extension flange can be uneven and affect accuracy. All the BR guys do it, and I do it to every upper I build or ever have apart.

Guess I should add... I use the finer 600 grit compound. Many use 200-300 but I like the fact that the finer grit cuts slower, giving you more fine control and not cutting too fast, especially for newbies. I even run a little onto the insertion shaft and polish the inside of my uppers. Makes for one incredibly slick action right from new, not much different from lapping in a bolt action. Just be sure to thoroughly clean the upper before actual assembly.