I have 2 of these Black Dog I got from a ODT member
http://www.midwayusa.com/product/2694845174/black-dog-machine-conversion-magazine-ar-15-cmmg-ciener-tactical-solutions-spikes-sig-522-rimfire-conversions-22-long-rifle-25-round-polymer?cm_vc=S016ID793914
and 4 of these CMMG I got online...
So I purchased a dedicated 22lr upper CMMG, 2 CMMG 22lr mags, 1 ProMag 22lr mag and a plum crazy lower. The thing shoots great. The CMMG mags operate pretty well, occasionally it will FTF, it seems to do it more when the mags get low, 1 to 3 rounds left. I think the follower pushes the round...
In case anyone was wondering about cheap ammo.
I bought another AR last week off the ODT board. I also had some ammo I purchased to run and see if my original gun was particular about ammo before I bought it in mass. I decided to shoot the new rifle mainly because it has rifle feed ramps...
Send Blackhawk and an email and they will tell you exactly. If I recall correctly they replied to my request pretty quick, same day I think. I had a Sig SP2009 that they didn't list.
I use this for my M&P9. It fits tight, has positive retention both on my belt/pants and the pistol. The little lever that releases the pistol is easy to use and well positioned. I highly recommend this holster.
http://www.blackhawk.com/product/SERPA-CQC-wMatte-Finish,1145,1410.htm