I agree w/DWalt

The 375Win is shorter than the 38-55.
The 375Win is shorter than the 30-30.
30-30 brass is plentiful.
The 30-30 is a perfect parent case for the 375Win

Expanding 30-30 to 375Win should leave you with an acceptable length case if not one that will need but a couple .000" trimmed from it.


So what if it doesn't say '.375 Winchester' on the case head..

Find a set of FL dies in 375Win and make all the brass you'll ever need for that rifle.

....Or sell the rifle if they've become collectible$$ and you don't want to bother with the ammo situation.
Buy something else more ammo friendly.