Need comparison info .300 Ultra mag/.404 Jeffery.


Well-Known Member
Dec 25, 2001
Central Washington.
Here is my question,Could on form his own .300 Ulta Mag brass by necking down say a RWS .404 Jeffery case?..What I'm looking for is some quality brass for a .375 Ultra Mag seeing that the .375 Ultra is a necked up .300 Ultra case..Am I in the ballpark here?...
If you have a lathe to turn the rim down you can make your own brass from 404 Jeffreys. The case for the RUM's is basically a 404 with a rebated rim to fit a standard magnum bolt face. The other option would be to have your gun's bolt face opened to accept the Jeffrey and have the gunsmith set the barrel back and rechamber for 375/404 Jeff.

It probably would cost prohibitive and not worth the money IMO to do it.

Sorry to hear about your father, I lost mine to cancer not that long ago. Hope it all turns out well for you, my prayers are with you.

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