Questions about my first AR build???

[NugginFutz]

The concept is the same for the AR15/AR10, however, you can fabricate your own lapping tool by cutting a culled Grendel case in half, place a spring in it, remove your ejector from the bolt, then lap the bolt to the extension by cycling the charge handle back and forth. When I do it, I make sure the CH latch does not slide over the latch notch on the upper to reduce wear there (steel vs. aluminum).

These are common gunsmithing techniques, and pretty standard on NRA hi-power rifles.

You mean something like this?
[ATTACH=CONFIG]4249[/ATTACH]

What type of spring did you select?