Model 70

[G. Wells]

Not a 375 H&H chamber. More likely a 375 Ackley Improved as it doesn't appear to have the double radiused shoulder of the 375 Weatherby, although that's difficult to tell from the picture. Not a 378 Weatherby as that is a larger case.

[edgarspencer]

Positive that's a Ackley Improved .375 Mag.

[C.O.B.]

Mills take a factory case and compare it to a fired one. I agree with the others that it looks to be whats called an improved 375. P.O. Ackley did this to a number of cartridges. I once had a 257 Roberts AI and have a 7X57 AI. You can shoot factory 375 ammo and the shoulder will be fire formed to the improved version. This modification eliminates any collector value however.

I have a great plinking load using a 200 gr bullet and 4227 for my Pre 64 M70. It will flatten a deer