Given that 7 RUM brass is $2 to $3 per stick, IF available. And given that it is the same case length as 7 STW and 300H&H brass. Any reason that 7 RUM brass could not be fire formed from 7 STW, or, necked down 300H&H brass ?

Have a quantity of both of the latter on hand. And disinclined to spend $2+ per stick for the former... Do-able? Caveats?

Ultramag is beltless

O.K. then. No-Go on that.. Thank you !

IIRC the parent case is 404 Jeffrey?

I did about 15 minutes of poking around regarding case lengths, shoulder diameters, rim diameter, etc. Did NOT even think to look at belt vs beltless... Feeling really dense over that one... Oh well...

Get .300 RUM and neck them down to 7mm.

I’ve done this several times.

Beltless AND rebated rim.

I did also when I owned a 7mm RUM.

I appreciate the input on necking down the 300 RUM brass...