I think this is your best bet. You have the brass and will fit the 3.5” limit. Just expand and load , no worries of fire-forming. The right powder and barrel length will easily out run a 7mm Rem Mag.I have a few hundred pieces of 270 weatherby cases I could form to 7mm Weatherby Magnum
Lol, I was just searching for 7mm Wby brass in stock....nothing.I think this is your best bet. You have the brass and will fit the 3.5” limit. Just expand and load , no worries of fire-forming. The right powder and barrel length will easily out run a 7mm Rem Mag.
I went with the 7mm Mashburn a few times. If 3.5 is your max it's really as easy as getting the rifle chambered and having your smith throat the rifle for the bullet you intend to use. I wouldn't sweat a 3.5" magazine on a Mashburn too much. Warren Page used a 7 Mashburn to kill alot of animals with that rifle constrained to about 3.4"..the 7mm mashburn would be pushing the 3.500" coal limit . the Mashburn has about the same water case capacity as the 7mm LRM . the Mashburn will run with the STW . the STW will have trouble with the 3.500" coal limit . I think sammi length is 3.6xx" for the STW . the LRM had a problem with poor brass quality , I'm not sure if that's solved . the Mashburn is formed from 300 win brass . everyone sells 300 win brass .
I run the 175 AccuBond LR bullets at 3.500" . 76.5 grains of H1000 gives 3145 FPS .
I run the 175 sierra SBT bullets at 3.415" . 71.6 grains of H1000 gives me 3000 FPS .
I'm pretty sure Scotty has his throat a little longer than I have mine .
if you're not worried about a wildcat cartridge , have you looked at the Shermans ? Rich Sherman has a few different 7mm's . he has brass with the correct headstamp , no die forming , or fire forming . he has die sets . it would be an easy one to work with . the only down side I can see is , I " THINK " Rich has all the stuff tied up . you would have to buy everything through him .