Thread: Tikka T3 .270 COL reading .005" off standard COL

The problem with pinching the case neck is that when you close the bolt forcing the projectile into the lands, the projectile can stick and actually pull out despite the pinched neck meaning your measurements despite being consistent may not be accurate.
A better way is to put some red loktite on the inside of the case neck of a fired case then sit your projectile in leaving it as long as possible then chamber that round and let it sit for 3-5 minutes after closing the bolt (allowing the loktite to set) then carefully eject and measure.
This should give you a reasonably accurate measurement for your jam length. As long as your mag length is shorter than your jam then that's where I'd start. Otherwise just start at SAAMI spec. Hope that helps and makes sense.