260, After rereading your post, I would agree with ray h don't trim, But I would use a good stiff load with bullet to really move the brass, I do a lot of case forming (since I cant be satisfied with standard cartridges) and used to trim to spec length before fire forming, Just to find most cases actually shrink as they fill out, The day I realized this after converting 200 shiny new FC 223 cases to 7mm TCU
they shrank from 1.750 to 1.710 after the first firing
and my chamber is 1.794 I went and looked back at all the different cases I make and how many were way short
gave me something to learn and do over.