Trimming before or after fireforming?

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I have 100 pieces of new norma brass and would like to trim them all uniform after fireforming, however by shooting these fire forming loads untrimmed the accuracy is not going to be there like if they were all trimmed to the same length. I would prefer to have accurate loads I can use while fireforming but would also like to do my trimming after the first firing. Does anyone trim before and after the first firing? Please explain what your process is for this. Thanks.

 

[varmintH8R]

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!