Shim help

[ccampo]

I have a Spikes Tactical ar15 . I am making it and sbr. I have a 10.5” BA barrel and a Black Rain handguard that I got second hand. I am confused on the barrel nut diameter. The handguard did not come with its shims. It needs some shims. I ordered some at work to day that are 1 inch ID. Well I got home and realized that they actually need to be around 1.2-1.25 inch ID to fit over the threads of the upper. Can someone give some advice on this? The shims I see that are that size say .308 only.

[Todd.K]

The barrel nut tightens against the barrel extension. So 1" ID is correct.

[ccampo]

The ID of the barrel nut is around 1.25 inches. The OD of the upper threads is also around 1.25 inches.

[308sako]

shims go on the barrel extension interfacing with the face of the upper, not past the threads...

[GH41]

The barrel nut tightens against the barrel extension. So 1" ID is correct.

Let me see if I can draw him a picture... Insert barrel into upper reciever, install shim/s if needed and screw on the barrel nut. The shim needs to be 1.00 ID and 1.17 OD. I have no idea what thickness the index marks on the barrel nut represent. Dropping Black Rain an email would have saved some bandwidth.

[jsbhike]

shims go on the barrel extension interfacing with the face of the upper, not past the threads...

That is how Bison Armory shows it in their installation video necessitating cutting the shims to go around the index pin.

While it will work, there is no reason to do it that way assuming you aren't trying to change the relatioship between the barrel extension feed ramps and the upper.

The shim goes between the muzzle side of the barrel extension shoulder and the barrel nut interior face.

My head finally popped out of my ass and I remembered a good shim installation demonstration!

[GH41]

Here is a Blackrain specific video. https://www.youtube.com/watch?v=c2LheKcaezI