AR-15 magazines/different calibers?

[theleo]

I thought the fireball neck was thinner?

I'm not a Blackout expert but looking at the specs the 221 should have the thicker neck.

[grundy53]

Give it a break. Quit derailing this thread.

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[dontgetcrabs]

I meant after resizing.  Compared to a shortened and resized 223. I think the neck would be thinner on the formed fireball case vs the formed 223 case.   

[theleo]

Give it a break. Quit derailing this thread.

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Ohhh, come on party pooper. If it hadn't been for the derailment you'd have passed rite on by.