Re: .22lr conversion on an AR15
I agree with other opinions of the conversion kits. They are less accurate, foul the absolute crap out of the chamber, upper, lower, barrel, and gas tube. Id say they are about the same on reliability. A dedicated 22lr ar like m&p15-22 is going to cost 2-3 times as much as a conversion bolt and a few mags. If you have an aversion to cleaning, require accuracy above 2-4 MOA, or want to use a 22lr suppressor the conversion kit will work fine. But you will have to clean the beejesus out of it after you shoot 22lr.
Short story:
I shot about 200 rounds of 22lr with a few friends out of my adams arms piston upper about a year ago. To use the cmmg kit in a piston upper the op rod must be removed. With the op rod removed all the gas and fouling coming from the gas port just shoots straight up into the top of the gas block. Well after 200 rounds I decided to put the op rod back in and shoot 223. Well The op rod wouldnt go back into the gas block. I examined it, shoved a brass cleaning brush in there and scrapped away at it for a few seconds, still nothing. It was like an invisible object was keeping the last (largest) part of the op rod from seating into the gas block. Well after inspecting it multiple times I concluded that the fouling from the 200 22lr had accumulated on the top inside of the gas block. It was such as small and uniform amount i didnt notice it the first few times. I took a steel cleaning rod and scrapped at the carbon and lead deposit. Try the op rod again, nothing! Scrap scrap scrap for minutes, try op rod. NOTHING. So I decided to shoot 1 round of 223 with the op rod removed. It completely removed all the lead and carbon from the gas block and the op rod dropped right in.
Conclusion, 22lr can foul the ever loving crap out of your ar15, however the pressure of 223 is more than enough to clean out all the junk you cant either reach or move with a brush.