I know how to fireform brass as I have been for over 20 years,
around 15 years just with the 300 whisper.
I made a 357 sig in a blowback AR a couple years ago just to use sub
ammo and found that the brass would blow out to easy when i used a can so I removed the barrel and made it a 40sw.
If the 300 whisper works as a blowback then great!
but I'm thinking there may be problems so I'm waiting for this build to
get done and tested.
