I just finished forming some 223 brass into 300 Blackout for a coworker and what a pain in the [censored]. It's not that it's hard to do but very time consuming and I used a lathe for initional trimming. The case reminds me of a 7.62X39. The 300 better be a top performer to justify the case prep work to be fed thru a semi auto. I think I'm going to tell him for every finished piece of brass it will cost him the same in strait 223 brass for me. Seem like a good deal or should I get 2 pieces for 1 300 Blackout finished brass??

You could just tell your friend to buy Blackout brass instead of making it.

He can't find any

I dont know about how much to charge... my process is two steps longer than my 223 process.

I tumble
Resize without expander ball or decap
Cut to just over length
Neck size with Decap and full length die
Trim
Camfur and debur
Polish

I use the Lee precision trimmer with the brass on my cordless drill.
The trim camfur debur and polish all happen on the drill.

My thought is maybe 4 for 5... but 3 for 4 might be closer to cover costs.