curious about a pre-64 model winchester m70... its marked ".300 mag".... from the serial number the gun is a 1948 mfg... no reason to belive that the barrel had been changed, rechambered, etc... as all the other marking look original...and obviously the .300 winmag hadn't been invented yet.... pretty sure the gun is a .300 H&H... i've seen the later guns marked with the H&H, did winchester wait till the .300 winmag came out before it changed the marking, and differentiate between the 2????..was the H&H chambered at the same time as the win mag???....

I'm no expert on these but from Rule's book...
The 300HH was stamped 300 Magnum on rifles up to mid 1950 and then changed to 300 H&H Magnum from there forward.
The 300 WM was first chambered in 1963, the last year of the pre 64's.