Whats the best (most idiotproof/reliable) .22LR upper / magazine combination for an M16 lower ?
Full auto capable of course.
Yes I saw the thread on the CMMG upper and magazine problems so was looking for a sure fire reliable alternative.
I have an unfired military kit.
Are they OK ?

To the best of my knowledge, the .22 conversions adopted by the U.S. military (Army and Air Force adopted different units) are not capable of full auto operation without modification(s) or the presence of a malfunction of some sort.

Best of luck.  MHO, YMMV, etc.  Be well.

The military kits are not FA capable, as noted.

If you have a genuine factory full auto, like a real Colt M16, the CMMG or older Spikes or Ciener conversions, with the proper full auto parts, are pretty damn reliable.

I've never had an issue with my Ciener, CMMG, Black Dog or S&W M&P15-22 magazines. It's always been dead nuts reliable for me in my factory FA, and was always iffy in my conversion AR-15 lower. Using it with a DIAS was a crapshoot, though I could find combinations that worked well for a particular afternoon. It pretty much always goes back on the factory lower if I want it FA and I want it reliable.

Nothing in 22 full auto is 100% surefire reliable - too much variation in the ammo, IMO.

I like the better mag adapter that allows me to use S&W magazines, including drum magazines.

My gun runs like a top.

Dedicated Cmmg upper with a .22LR barrel and the full auto trip.
Better mag adapter for M&P 15-22 mags.
Use good ammo like mini mags.
Keep it clean!

Will run like a top.

I  have a M231,  runs great,   not had any issues with the 10 round mag inserts ,  but not full auto


I have a Ceiner kit that runs like a top on full auto,

This (CMMG 9" barrel and bolt/frame/collar assembly, etc. on a generic AR upper receiver):


with the only modification being "throating" the bottom lip of the chamber like so:


has worked great.

With respect to M&P .22 mags - I have never used them but at least one ARFCOMMER has reported that with use, the mag lips wore out; and they have therefore, switched to BDM mags with steel lips.

Best of luck with whatever you pursue.

MHO, YMMV, etc.  Be well.

I have a short piecemealed CMMG mixmaster upper. ( I forget just how short - maybe 8"? ) The last time I decided to beat my head against a wall with it, I got mixed results. Oddly, it seems to run FA with a suppressor, but not with a brake or bare.

I need to get it back out to the range sometime with another can and test it some more.

Thanks for all the responses.