I own a pre-64 M70 in 300 H&H, it's a rifle I've owned for a long time now and it being the sweetheart it is, I'd hate to have to part with it. . The long tapered cartridge goes through the rifle smoother than a teenager goes through his allowance and it groups in tighter than most of us are capable of. . But there's more to the rifle than that . . the stock design of the pre-64's (NRA stock design) makes the rifle so shootable as the recoil is a pleasure even with the steel buttplate. . The whole outfit is just a joy to have. .
I also have a pre-64 M70 in 338 WM which is the same parent cartridge as the 300 WM just producing a bigger hole and more energy. . I like it as well and have no problem hunting with it. . I have to admit, I'd sure like a pre-64 in 300 WM but can't justify paying what is currently asked for one. . Besides the fit and finish in 1963 was just terrible, especially the checkering.
Now, back to your thoughts on a new M70 in 300 WM.. Sometimes we can understand things better if we know how it works. . Winchester in the late 1950's and early 1960's were looking for a way to make money again building rifles and shotguns. . They decided one way to save on cost was to shorten the action while maintaining the punch. . In the late 1950's they fattened and shortened the 300/375 H&H case and came up with the 458 WM, 338 WM, 300 WM and the 264 WM all sharing a shorter case being called a short belted magnum. . What better cartridge to shorten up than the 300/375 H&H. . Expand out the shoulders, shorten the neck and overall length and there it was; the 300 WM replicating the 300 H&H magnum. . The 300 H&H, in my view, is a better all round cartridge eg. more efficient with powder, able to handle lighter bullets with supreme accuracy, easier to reload, etc. . All kinds of reasons to prefer the H&H, but, the 300 WM is no loafer and Winchester improved the loadings and bragged it up as superior to the H&H to help with the sales. .
The moral of all this is; if I wanted a brand new M70 in 30 caliber magnum I'd be buying up one in 300 WM and would shoot the hell out of it. . No problem with wanting a 300 H&H, every once in awhile a pre-64 M70, in 300 H&H, comes available and the extra money you'd pay over a new M70 would most likely be quite a bit less than the cost of converting a new one over to 300 H&H. . One thing for certain, the pre-64 would be a better investment if you need to sell out.
Anyways, a bit long winded, but life is good and I'm sure you'll be fine with whatever you decide.
