Don,
I believe you will be cutting down longer hulls to form the 2 7/8 shells anyway so proceed to trim them to the 2 5/8" instead. Since you are going to be loading 1oz loads, filler wads will be required. If you are using fiber wads for the fillers split them down a little to make up the proper crimp with a folded crimp. The same powder loads can be used and the slight variation in your filler wad won't make any difference to your pressures. If you are using a roll crimp with your loads somewhat lower pressures can be achieved and the length of a shell cut to length for a 2 7/8" load with a roll crimp will be easily accommodated in your chambers without problems.
If you need data for 10ga loads email me at jvlape@cox.net and I will give you a data dump which will fill your requirements.
