I understand that they are very close to the same, but some manufacturers are offering a re-chambering from 300/221, 300 whisper ect. to 300 blackout. That means that metal is being removed from the old chamber, therefore the 300 blackout cartridge is bigger (somewhere) and should not fit in a 300/221 ect. chamber, but a 300 whisper should fit in a 300 blackout chamber...............At least that's what I'm thinking. I guess I should research reloading dies and see which set is cheaper, then get a barrel to go with my dies.
swampf0x
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