What do you need to trim shells for?? Never done that before. Are you trimming 3" shells down to 2-3/4"??
There are a couple of reasons why. If you roll crimp shells you need to trim sometimes, ie slugs, hull's to long for load etc.
Roll crimping is usefull for load identification, to lower pressures, load capacity etc.
Some of the older doubles can only take 2.5" shells, so hull trimming is neccessary even for a fold crimp.
Shorty loads, i can get 7 2" shells in my A2000.
I do trim 3" hulls from 2 3/4 down to 2".
Roll crimping is a change of pace from the hum drum of cranking a handle.
As my old man would say, "There's loads and reloads"