Is that a word???:shocked: The books will tell you it headspace on the case mouth. IMO, & others that reload this round a lot, it headspaces on the tiny shoulder as all bottleneck rounds should. Reality, it probably is held in place by the extractor BUT, get the shoulder worng & the round will not fit. It will be too far forward & not chamber or too far back & w/ a sloppy ectractor, will not fire. To date, I think every manuf has it right but RCBS, the sizing die used to not get the shoulder right & had to be milled off a few 1000ths to get the shoulder right. I use Dillon dies. Screw the sizer down to just allow a sheet of paper to pull out & they are perfect in 4 diff 357sig bbls; Sig, Barsto, Glock & EFK.What do you use to verify headspace on your .357sig reloads? Should I get an LE Wilson case gauge from Dillon, Hornady headspace gage, just use the chamber in the barrel to assure fitment?
I've read the Hornady headspace gage can give varying reading and is made of soft aluminum that distorts over time.