Home Forums Hunting & Shooting AR and Tactical Rifles Tac 20 build (pic heavy)

One more update before the holiday weekend; got the barrel threaded and chambered, pics below.

I like to stop after the first light pass with the threading tool (only a few thousandths deep) to double check the thread pitch; easy to correct it now if it's wrong, but a lot harder later.


Threads are complete so the barrel extension threads on with a close fit. This is also the time to adjust the barrel shoulder to "time" the barrel so that it points either up or down, rather than off to one side; just a little accuracy trick that usually gets skipped in production barrels.



Now time to ream the chamber. This reamer has a floating pilot, so I chose a pilot that is a close fit to the bore. The Caudle rifling in this barrel has a larger bore (not groove!) diameter than standard, at .1993", so I used the largest pilot available at .1986"; not quite as close fitting as I'd like but close enough to work well.
With a small reamer like this, there isn't a lot of room for chips, so I only cut about .060" at a time and then retract the reamer to clean the chips out. It does get tedious, but gives better results than just ramming the reamer into the bore till it's done. I use lots of cutting oil on the reamer.


Part of chamber reaming is setting headspace, this is the equipment needed to do that. Go/no-go gauges, a good caliper (and also feeler gauges, not shown), and the bolt and barrel extension.


Setting headspace in AR barrels is actually pretty easy when done this way - by screwing the barrel extension on over the bolt and Go gauge, the gap between shoulders of the barrel and extension can be measured. This measurement shows that I need to advance the reamer another .3585" deeper to close on the Go gauge.


Headspace is now correct, with the bolt able to close on the Go gauge (as shown) but not quite on the No-go gauge. In this cartridge, the difference between the Go and No-go gauges is .003", so I chambered .002" deeper than the Go gauge. The sizing die will be adjusted to match that setting of course.