Brent,
Please check the magazine measurement survey I did a few months back
http://forum.lugerforum.com/showthre...hlight=mec+gar. You will see that Mec-Gar is not substantially different in size from most original Luger magazines--average, within a few thousandths of an inch. The only magazine I measured which is substantially smaller was a Mauser blued-tube aluminum-base stick-eagle/63, .03 in. smaller than the others. This magazine actually falls from the gun when the mag button is pushed, and is the only magazine I have which does so.
The model paint idea is a good one. On the other hand, if this gun is not a Luger for shooting, I suggest putting a period-authentic magazine in it and leaving well enough alone.
--Dwight