Yep, plus they are better built and hold 5 more rounds. Any .45 mag loader will make loading easy. I got several from Numrich for like $7.Maybe... but why? The greezer mags work just fine... a bit hard to load by other mags standards, but even this can be overcome.
Those guys who were going to make the multi caliber MP5 used UMP mags on the prototype they had?I personally know this has been done/tried by some of the best but there were significant feed issues. Bottom line---didn't work. The Grease Gun mag conversion works just fine if the builder HAS THE GUN WITH HIM. The specs for modifying are general specs and if the builder has the weapon he can work them as needed. ALL of my mags work in mine.