I was at the range with my 20 and my uncle had his new gen4 21. Just for kicks we dropped my LW 10-40 conversion in his gun and it ran great with The 45 extractor and duel rsa. Next I dropped in my oem 10mm and ran some 180's at 1250fps through it. Still ran great but I could tell the extractor wasn't holding right because the emptys where going all over the place. My thought was if someone had the balls and a mill you could take a couple thou off the sides of the lug in the back of the barrel, switch the extractor and mag and be able to shoot .45. I'm not really wanting to shoot a crap load out of it, but it might be nice if things where bad and that was the only ammo you could get your hands on.