Good, informative test, thanks.
Also, the Mini-Mags are "gilded lead" and may not be as hard as the FMJ surface on the .25ACP bullets.
I may someday get a pocket-sized modern .25ACP that is safe to carry with one chambered. For now I have to be content with my 100-year old Colt Hammerless Vest Pocket pistol, it's amazingly accurate out to 25 yards (haven't tried shooting it farther).
http://thefiringline.com/forums/showthread.php?t=504371