Yeah, I've been doing alot of research on the G&G and from what I know is that its only compatible with its own mags, I just read
here (read mag suitable for) that it was compatible with the G&G, but I guess that it was assumed that since it was a M14 mag, it was compatible with all M14's. Perhaps a TM is the better choice in this case, although the walnut wood stock on the G&G is really nice.