Hey, I will say this for you guys converting 5.56 brass to 300BLK - there are steps you need to hit, every time.
1) Cut (in whatever manner) the 5.56 brass at or right below the shoulder.
2) Do not final-size it yet.
3) Chamfer it in and out, so it doesn't tear up your 300BLK sizing die. You don't want rough-cut edges going through your die.
4) Once it's resized to 300BLK, THEN you trim to the proper trim length. Max length is 1.368". Trim-to length is 1.363".
If you cut your 5.56 brass at the shoulder, then trim it down to 1.363", it's gonna be to short once you resize/reform it. That process drops a few thou off the overall brass length...
Now, those damn PNW 220 subs shot fine, EVERYTIME, through Dawn Marie's 14.5" carbine-gassed BLK barrel today... The damn things won't cycle reliably through my 16" carbine-gassed BLK, but they do in hers... :rant2: