I just ordered 1000 shiny new Starline 10mm cases to make reloads for my Glock 20. Naturally, being brand new brass, their overall length will vary a bit - Starline says from 0.984-0.991 in. I've never in my life trimmed pistol brass. That includes other cartridges I load, .40 S&W and .45 ACP. Trimming just never seemed necessary. Do you trim? If so, what does it do for you?