The only real way to know max is with a chamber cast and some pressure test equipment.
No need for all that. Your reloading manual will list a max case length. That is max. It will also list a trim length. This is commonly accepted as the min. There are those who cut shorter, but why??? I don't. Shorter affects your bullets ability to hold the bullet well.
You always need to measure your length after full length sizing. That is when the case is longest. A caliper works fine for this. Be sure to rotate the case to find the max length when measuring. Also, be sure the case head is touching the base of the caliper. Sometimes primer crimp or primer makes this stick up.