+1 for conv. kit…I however rock the Ceiner kit (with the metal clip):).
Was thinking about getting the conversion but got the dedicated cmmg upper 20" and have been very happy so far.
Shot over 1,000 rds and not a single issue. I would recommend getting the stainless steel upgrade. It makes cleaning and lubing very easy.
I am not saying that a dedicated .22 upper isn’t worth it and won’t pay for itself fast, but I chose the conversion kit route. I purchased the CMMG stainless steel kit 8 months ago and have put around 600 rounds down range. Biggest issue I have are jams (AR style stove-pipe). Can’t tell if it’s a feeding or ejecting issue however, as I just clear the malfunction and move on. Maybe next time I will investigate a bit more. I do however use lead rounds not the copper jacketed. I do shoot CCI mini-mag through occasionally and it runs just fine. I usually clean out as said before with some .223 or 5.56 at the end of a session and a heavier cleaning regiment afterwards as compared to only shooting 5.56/.223, YMMV.
I’ve run thousands of rounds through various uppers using my Ciener kit, most recently 800 + rounds through my BCM EAG upper, which still shot a 3 inch 100 yard group using Wolf 75 gr directly after running the .22 through, using an Aimpoint H1.
I use the same cleaning schedule on my barrels, which is never 
I’ve never had a gas tube block up.
I’ll wipe out the upper and lower a bit more, and throw more lube on, that’s it.
My original BCM 16" carbine upper (one of the first $399 ones) is still going strong after 12,000 rounds of various .223 and probably close to the same with .22 lr. I’m confident it will serve it’s new owner well (hopefully I can get him into a class soon).
My experience is that shooting .22 lr won’t effect anything.
CMMG carries various kits (levels) for the .22lr conversion. Which kit provided the best results? Any recommendations on a purchase?
Thanks