Thread: .300 BLK in .300 Murmur ?

Originally Posted by Friwi

@Wingman
I think it is the other way around.
I have both a 30-221 reamer ( could not buy a whisper at the time in early 2000) and a 300 black.
The whisper is 8,58mm at the neck while the black is 8,61-62 ish.
My rifle in 300 whisper can not chamber certain commercial rounds in 300 black.
I had to neck turn 223 brass when I first started loading for it.

Hornady went around that problem by manufacturing their rounds that would fit in the 300 whisper and there fore also in the black out.

Yeah there is probably a bit of variation between reamer grinds too from the various manufacturers. The .300-221 reamer was its own thing again, it was designed and ground smaller to use necked up .221 Fireball brass which meant the necks were thinner than when you used the body of a .223 case. Redding made custom dies for the .300-221 which were slightly different to their later .300 BLK dies too. Hornady were the only ones licenced by JD Jones to make the .300 Whisper TM dies.

Heres a factory AR15 .300blk chamber and a case fired in it that was pushed forward 120 thou using an original JD Jones .300 Whisper reamer.
Most modern ground reamers like in the last pic have now been revised and changed to suit the .334" .300BLK neck dimensions as is is now the SAAMI spec and avoids issues with factory ammo.