Consider the 30x57 which is just a shorter chamber done with the 30-06 reamer. That would give you an easily made wild cat with the capacity of the 308W thus avoiding the potential use of 308W ammo in it. The 30x57 maintains the tapered case that the single stack magazine is made for so feeding isn't a problem. Cases are easily formed from 30-06 family of cartridges of from factory 8x57 cases. Reloading dies are simply shortened 30-06 dies. The 30-57 case maintains the '06 length neck also which is best for a variety of cast bullets.
I've rebarreled several M91s to the 30x57 and 35x57 cartridges. They are excellent cast bullet cartridges and also work well with jacketed bullets.
Here you see (left to right0, the 308CBC, the 308W, the 30x57, the 7.65 Argentine and the 30-06.
Attachment 314188
Cases formed with 30-06 shortened die; 30x57 on left, 35x57 in middle and 30-06 on the right.
Attachment 314189