I use a Lyman Universal Trimmer, which uses a collet to lock the case head in place, no shellholder. They also make one that uses an ordinary shellholder to hold the case. This allows you a lot of options. The hard part is probably getting the pilot for the trimmer head. Most of them stop at the 45 caliber range. You may need to request a special order on one.
As far as trimming, I have fired mine several times, and I have not seen any evidence of them stretching. With smokeless powder it might be a different story, but I use BP.
Hope this helps.