What you've found is an example of the fact the difference between case length and COL varies from cartridge to cartridge, so the cannelure position has to be aimed at one such combination, whether it is shared among cartridges or not.
Yes that mil-spec MK 262 MOD 1-C, MIL LMNOP stuff is crimped . Yes it’s designed for the military but they sell it commercially as well . I have a duplicate-ish load using the 77gr smk w/cannelure and AR-comp . Shoots really good from all my AR’s ( not that I have more then 1 ) and shoots lights out with my 18” build it was worked up for .
Before anyone thinks to get cute , I consider anything loaded with a match bullet a match cartridge . I don’t care how it’s marketed , if Federal gold medal match was marketed as a plinking load , it doesn’t mean it’s not a match load as well .
