While I can't give anything of info to your topic (I have a couple MK23 holsters at home, I can give a try in a couple days when I get back), I can give you info on a perfect mag pouch for the M11 mags.
http://www.oneshottactical.com/merch...Category_Code=
The longer one my gf won at a game recently, was said to hold either a baton or an MP5 mag, easy enough to see no MP5 mag will fit in there at all, so I left it in my bag for a month untouched. Then I dug out my M11 figuring I'd give it some attention, lo and behold the mag fits in perfectly, but better yet there is no pressure on the top round (bad design flaw of KSC M11 mags, top pressure makes BBs spluge out fast). Now I want to buy a couple more mags for it and see about gaming it more.