First thing I'd do is make some measurements to determine the location of the locking "cuts" in the magazine body and compare the measurement of the ones that work against the ones that don't. It's possible the locking slots on the mags are not located at the same point on all of them, or better stated maybe they are not all the same dimension, as in width and depth.
[This message has been edited by sensop (edited May 19, 2000).]