I want to be able to shoot .22 out of my AR so I can get alot of CQB practice cheaply.  If I spent as much as a dedicated upper costs it would defeat the point.  So that said, what are the drawbacks to this type of unit?  Is their one beside the Ciener I should be looking at.  Are the stories of shooting the .22 bullets from a .223 upper and getting lead in the gas port true.  If so, is it a problem?  Is there a fix?

I have not heard any reports, or experienced any problems with the 22 LR Ciener conversion kits, in getting lead into the gas port.  It could be theoretically, or on the other hand, itmay just be a "second barrel advocate's" idea of a possibility. If you have an article claiming this, please post it or link to it. You might have to wipe off some residue, but if the rings are tight, how does it get into the gas port?? You do need to clean the barrel before shooting .223's after shooting the .22 LR's. The round-nosed, soft lead 22's do leave residue in the barrels, but they also feed well from the Ciener mags into the ramp, and most .223's are FMJ. If you plan to shoot both calbers the same day, carry a bore snake and clean the barrel before using the .223's, or shoot the .223's, then the .22's.

Mike

I saw a review on a web site where they did clog the gas tube.  Don't recall how many rounds it took to do it though.  I might be able to find it again.  The "conventional wisdom" I've heard is to shoot a couple .223s every 500 rounds or so of .22 and you'll be fine.

Not only does it get the barrel dirty, but the gas tube will blow lots of crap all over the inside of the upper too.  I'd want to do a full cleaning after the .22 before shooting .223s again.

The Ciener is popular because it's the only one still in production, and the only one with hi-cap mags available (but at $150+).  If you can find one of the Army M-261 kits they're also good.  

If your CQB practice includes mag changes you can have the bodies of those worthless USA mags welded onto the Ciener mags to give them the same feel.  I think the M-261 uses inserts in regular USGI mags so they'll feel just like real ones.

Edited to add: I found the bookmark for the review I was thinking of, but the link's broken.