Wouldn't that make it a 64A with the plastic mags?there's 2 style's of 64B mag's, the key hole mag such as above and another box style made of plastic....
if your 64B dosent have the spring loaded mag release at the muzzle end of the mag well then it uses the older (read obselete) plastic mag's...
Wouldn't that make it a 64A with the plastic mags?