Freak,Measuring from bolt face to the chamber’s shoulder datum any length at or between a minimum of 1.630” to 1.640” maximum is within SAAMI’s chamber specs.
SAAMI’s cartridge length specs measuring from case head to shoulder datum is 1.634” -.007”, or a minimum of 1.627” up to a 1.634” maximum.
If the chamber was cut to the SAAMI maximum length of 1.640” and a cartridge sized to the SAAMI minimum length of 1.627” gets chambered, then the resulting clearance between bolt face to case head is .013” (headspace), and all’s still within SAAMI’s specs, der …
Need to first find what’s your chamber’s length and then size cases to a thousandth or so shorter.
I settled on the lower side of this range because I wanted to be able to use factory ammo if necessary. When I first started this build five years ago, I measured some Remington factory ammo and found the shoulder height to be closer to the 1.630 than the 1.640 end of the range.