What length to trim..

bunch of original AA, to shoot thru a 2-5/8 chamber?

Thanks.

I've made these. I trim to 2 5/8 long(12ga).
I took a piece of electrical conduit (1 size bigger than the smallest diameter). Cut to the right length to insert shell and trim with a pocket knife. Using a wad for 1 1/8 oz., It worked fine with 1 oz.

I should add that you may need to trim the wad pettels back 1/8 inch with scissors, or compress the wad a bit which can be done safely to a certain amount. You need to read, comprehend and experiment.