Where can I find exact Mil-Spec measurements for an AR-15 buffering tube. I purchased a MagPul PRS-Gen3 stock and it doesn't fit over my buffering tube. I want to insure my buffering tube is Mil Spec

I just measured one at 1.12. I know the Mag Pul stocks are tight.

Nominal outside diameter for a milspec buffer tube is 1.145". They often vary from 1.145" to 1.150". One of mine is 1.148"
Nominal outside diameter on a commercial buffer tube is 1.167" (average).

I know the following companies make milspec buffer tubes. There are likely many more:
1. Brownells
2. DS Arms
3. DPMS
4. Bravo Company
5. High Standard
6. VLTOR Weapons Systems
7. Patriot Ordnance Factory (POF)
8. ALG Defense (Geissele off shoot)
9. Colt
10.Heckler and Koch
11.Spikes
12.Aero Precision