ddj, battue and BobinNH,
From an engineering standpoint the pre-'64 M70 is indeed inferior in its gas handling in that, in comparison to the Mauser M98, for example, it lacks the internal gas collar (C-collar) that mostly surrounds the bolt head, the thumb notch that allows gas to vent from the left lug raceway, and finally the bolt sleeve flange that deflects gas away from the shooter's face. Of course, commercial Mausers like the later FN and Zastava that have the H-collar seriously compromise gas handling by providing a big hole leading directly into the left lug raceway.
In fact the M70's bolt head design is very similar to the Springfield 1903, which was probably the model for the Winchester 54 which in turn led to the M70. Incidentally, I recently looked at a Kimber 84 and it has a screw-in C-flange that sits where the internal gas collar on the Mauser 98 is, and presumably is intended to serve the same function.
Having said all that, however, it's mainly something for rifle looneys to argue over, just like medieval theologians argued over how many angels can dance on the head of a pin. From a practical point of view, given how good modern ammunition is, worrying about gas handling is equivalent to worrying about the chance of getting hit in the head by a meteor. It's probably happened to someone, somewhere, at some time, but really... At least, that's my opinion, I could be wrong... :-)
