I'm doing my reading on reloading and different cartridges, and it seems a few things which you'd assume were pretty set are largely "guides" ?
COAL for example...
.308 COAL is 2.8" according to most people, ok great.
But then you have rifles where the magazine is too short to fit 2.8" cartridges and they have to be shorter.
Then you get rifles where for your hand loads if you want the bullet to be just off the lands you have to seat it higher making the COAL longer that 2.8"
That's just one cartridge example obviously, but seems common enough across the board?