converting .223 brass to 300 AAC

[chiao123]

What is the exact length .223 brass has to be cut down before i put them thru the dies for 300 blackout for .223 to 300 aac conversion? On ammoguide.com they list 300 blackout case 1.368.

http://ammoguide.com/?catid=808

[thehouseproduct]

A lot of us cut it long, form it and then do final trim as 300BLK.

[Dacapster]

Yes, form and trim in a whisper trim die to @ 1.4 then trim to final length.

[Ned christiansen]

I have found the amount of length growth in forming the neck is pretty predictable--- about .009. I cut them off .010 short and have not had to re-trim after sizing.