Headspace Trick Custom Barrel

I love Gunco. The ideas and positive input for builder on all levels. I am sure this isn't an original idea but here goes. When I chose to use a custom barrel that needs chamber reaming or has an existing chamber this is how I set for precision headspace if extra stock is on OD. First I assemble the Bolt and Carrier. Insert these in the trunnion. Then depth mic the front of the trunnion to the face of the bolt (double check several times). Write this dimension down.( Example .750) When I turn the barrel in the lathe leave material for a shoulder on the trunnion diameter. Insert GO gage in the clean chamber and cut the shoulder back to the dimension recorded earlier to -.001 max by depth mic from the end of Go gage to shoulder (Example .749 to .750 ). Depth mic with the NOGO, the example dimention should exceed .752 (Example .749 +.003) . If your lathe doesn't have DRO then use an indicator when cutting shoulder. When you press the barrel in the trunnion flush with the shoulder, headspace should be correct (check it with gages before drilling/reaming trunnion locking pin). Note that all of the above numbers are Examples and adjust for your use. This is not meant for PNP (plug n play) builders if in doubt don't. It works for me. HTH