I bought a series of plugs from Sinclair International that allows you to get the exact maximum case length. You shorten a resized case until only half the neck is left then slip in the proper cal. plug, then carefully insert it into the chamber, remove & measure. Then you have the max case length for your rifle.
Also, I've never tried them, but RCBS makes a resizing die that controls case length so no trimming is required. Don't know how that works(?)