I have a CMMG kit, but I also have the dedicated CMMG 22lr barrel. It runs flawlessly. You will never have real accuracy with a .223 barrel shooting 22lr. The dedicated 22lr barrel is 1:16 twist and .22 bore. It is also chambered for 22lr. Makes a big difference.
CMMG makes the 22lr AR barrel in 16" or 9". I haven't seen any others. The 9" is out of stock most of the time. I use the 16". It is one of my favorite AR's. It never jams, and is very accurate with a little Nikon scope. I mostly shoot it suppressed.
I run a ciener kit in my 10.5” sir. I use it for plinking on 6” plates, and with bulk back I have no problems dining steel out to 50 yards. A dedicated 22lr upper will give you better accuracy for sure.
also check out: https://www.22mods4all.com/ar-22-22lr-trainer-series/
I ran a conversion kit with a 16" 1/9 upper for a while before building a dedicated rimfire AR. The conversion was good enough for minute of soda can (about 3-4") at 50 yards. Not terrible. The dedicated carbine cut that in half.
Don't forget to run a few 223 rounds through after firing lots of 22. I clogged up my gas tube or port in the bbl after shooting a brick in 1 day & the next time I shot 223, got lots of jams. Now it's a dedicated 22 upper since I don't trust it anymore.
I have a DPMS .22LR upper, and it works pretty well. Reliable enough, fairly accurate. I also have an S&W M&P22 as well as a Colt/Umarex .22 M16 (A2 style, 20" barrel). The Colt/Umarex is the most reliable and accurate semi-auto .22LR I've ever fired, bar none. Easy 1" groups at 100 yards with the right ammo, and never a malfunction with good ammo (primarily Mini Mags) and cleaning. I'd buy one in a second before buying another .22 upper.
I've never tried a conversion bolt setup for the reasons mentioned above. I'm pretty sure you'd get a fair amount of leading into the gas system that would be a pain to clean out, and of course there's no way it could be properly accurate. To me, the whole point of running .22LR is for the cheap ammo, but if it's a pain to switch back and forth and inaccurate, what's the point?
I have an old Atchisson conversion kit from way back. Worked fine, with both of the little stick mags I have for it. Very dirty and accuracy was the pits, but it was fun. It is a cheap way to plink for fun. If you have a spare upper I see no reason why you can't have some cheap fun with the kit as long as you keep it clean and run some regular rounds through it now and then.
I also have a M&P15-22. It has been great and have never had reliability issues with it. It is an older model with the quad rail and the non-threaded barrel.
I've also assembled a few dedicated 22LR AR15 uppers based on CMMG barrels and 22LR BCGs. Both are 9" (also had a 4.5" as well at one point) built on Aero Enhanced M4E1 uppers and they have run like clocks. Suppressed, binary trigger rip-saws, running both my old Atchisson stick mags, or with the 15-22 Mag-well adapter and 15-22 mags.
I have a complete lower built for my soon to be built 22AR but would like to get a heavy barrel instead of the pencil barrel. So far haven't found one in 22 caliber. I got my wife a Tacsol upper about 4-5 years ago that attaches to a standard lower but you can't find those anymore either.
So will build my upper from a bunch of different parts and hope they all work together.
Well, I bought a CMMG conversion kit w/ 3 magazines for $190 shipped.
It's going in my 10.5" AR pistol.
Was gonna buy a complete upper, a dedicated upper costs more than my whole pistol build did.
Thought about buying a HK 416 22 pistol and adding the adapter and a brace. Which would have been cheaper than a complete upper.
Maybe when Donny send me my monies