350 mashburn magnum
There is a .350 Mashburn short Magnum "made by shortening 300 H&H or 375 H&H and either necking 375 down or 300 up to .35 cal. " (after shortening the case of your choice.)
The second called the Mashburn Super Magnum uses the " full length 375 H&H case necked to .35 and blowing the shoulder out to 30 degrees" and takeing the neck down to .35...no shortening of the case here.
either version will launch a 220 grain to 3000fps......250 grain to 3000 fps..
and a 300 grain bullet to about 2650 fps useing imr 4350, imr 4831, with the 200 gr. useing the same powders, plus imr 4064 and imr 4895 as well.
....quoted words are from P.O. Ackleys books for reloaders... velocities likewise from same books.
hs4570.............your mileage may vary