Questions about my first AR build???

[customcutter]

All this talk about squaring up the extension to the upper is really deceptive. If the extension is installed on the barrel by the barrel maker that should be square. Then you put the barrel into the upper and when the barrel nut is snugged then torqued, it presses the extension flat against the upper receiver. There is no adjustment. If you find it off by the method LRRPF52 (Midway) said with the dykem to see the contact points, then using the compound is just to smooth and make it contact evenly.

Is that all your talking about doing? Mate the surfaces of the back side of the bolt lugs to the barrel extension with the lapping compound?

The procedure that LRRPF52 and Midway were talking about is to lap the bolt to the lugs inside the barrel extension.

Squaring the upper receiver to the barrel extension is another matter. The uppers are not always square to the bore. Brownells sells a lapping tool that can be used to square it up and make sure you have 100% contact around the upper receiver to the barrel extension. Then you get into, is the barrel nut machined square, are the threads on the upper machined square, etc, etc. It would be similar to "blue printing" a bolt action receiver. An awful lot of work to chase that last 1/4" of accuracy. Maybe worth it in National Competition, but not a hunting rifle.

I don't have a jig, or know of anyone that has one. I do have a large surface plate and machinist squares, so I'll check it that way. If necessary I can turn a jig on my lathe and lap the upper, but from what I've read the VLTOR's are machined pretty well.