Magnum base form die

I have a die marked MAG. Base form. Anyone know what this is for? it is RCBS made. RCBS doesn't know much about the old stuff anymore it seems when asking them.

Thanks. Attachment 296517

Just guessing, but I think it meant to size the belted magnum brass back to factory specs just above the belt.

Twenty to thirty years ago there was a small company that made collet sizers for the same purpose, they may still.

Robert

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Originally Posted by Mk42gunner

Just guessing, but I think it meant to size the belted magnum brass back to factory specs just above the belt.

Twenty to thirty years ago there was a small company that made collet sizers for the same purpose, they may still.

Robert

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Yup they are still around and they work very well https://www.larrywillis.com/

To the OP that is the first one I have seen.

Got any more pictures? Is it 2 pieces or just one? The Larry Willis die is 2 pieces. I think at one time he had diferent companies trying out his design maybe this was one of them.

only a single die. I sent a piece of 300 win mag through it. The base did size. As most of the belted mags diameters are in common this must be what it is.

I have Redding die that is marked "300 win mag body 5L" It sizes the body only on cases that are shorter than the 300, I've used it on 300 win, 308 NM, 264 and 7mm mag. Wont work on the 338, only 30 cal or smaller. Comes in handy now and then..