If you want handloads to fit your chamber perfectly, forget about making them to documented specifications. It's much more accurate to make handloads compare to a fired case from your rifle.
Works well with bolt guns but I would disagree with that when it comes to semi automatic weapons.
These mechanisms open up while there is still residual pressure in the barrel. This is intentional, the pressure is generally less than 650 psia, to avoid rupturing the cartridge, because this increases the time useful energy is available to operate the mechanism.
What it also does is stretch the case.
These cases were fired 23 times in a M1a. Somewhere in the middle of this I used small based dies and I always sized the cases to gage minimum.
My long case life is due to cartridge lubrication, I never had a single case head separation. I left either RCBS case lube on the cases, most of the time I rubbed Johnson paste wax on the outside of the case. The paste wax dried hard, did not attract dirt, under the temperatures and pressures of combustion the wax would melt.
Anyway, even though these cases were fired lubed, they stretched. The front of the case was sticking to something.
Therefore, you might not be able to make sense of chamber length in a gas gun from fired cases.
I have been using Wilson gages, but now that I know Dillion are stainless, go for the stainless. My gages I oil them before storage and I have to wipe them down afterwards.
