Re: Trimming before or after fireforming?
Are you fireforming for an improved chamber or just refering to getting virgin brass fireformed to your exact chamber?
In the case of an improved chamber, I trim to the listed "trim-to" length of the parent cartridge, firm form, bump the shoulder, neck size, and then trim to the listed "trim-to" of the improved cartridge if necessary.
If you are just fireforming virgin brass to your chamber (not improved) you may want to try this:
Determine your shortest piece of brass and make sure it is in-spec (longer than trim-to, shorter than max length). Trim all your brass to that length. After fireforming and sizing, you can then trim them all to listed "trim-to". Of course, you can always just trim them all to listed "trim-to" after every firing/sizing, and then you are guaranteed consistent.
Just make sure they are in spec - that is more important than anything!