If you look at AA wads like the 12AA, 12L, 12SL or 12 red AA you will see that they are all the same basic wad but each are different lengthen. If you substitute a shorter wad the load will fit into shorter hull. So you can find a safe 2 3/4" load, substitute a shorter wad for the one listed, to take up less space in a shorter hull, which you have trimmed to 2 1/2" and load a few. Send them to Roster or Precision Reloading if you need verification of pressure.
I have loaded a lot of loads which called for one Winchester AA wads and substituted shorter AA wad in shorter hulls. Find a load which calls for a longer Winchester AA wad in the 2 3/4" hull at the pressure you are wanting to load. Select a shorter version and try it. To verify if the load is truly safe send five or six of them out to be tested for pressure. That is the only true way to know what you have.
I like PB one ounce loads with the old style AA hulls and AA wads. I just use a shorter wad, cut the hull and crimp them in the normal way. Shame PB is gone unless you find an old stash like I did.
Go to the Hodgdon site and look at several different powders which are readily found like Clays, or PB. Go from there but don't forget to have your load tested to be safe.
