Burn,
Last year I finally purchased a Ceiner drop-in .22LR conversion kit for my AR-15.
At first it did not function. In fact, it ejected the spent casings straight up into the upper reciever causing the "Mother of All Jams."
So I checked to "techy" stuff on this board and decided to disassemble it, hone and polish all surfaces, and then re-form the magazine lips. When I had finished the necessary alterations I then began to try different ammo.
I discovered that my kit functions best with CCI .22 Long (not Long Rifle) ammo. Since then it's been ticking away with great reliablity.
Sure, it's not a tack driver - but it is good (unclean) fun! So, remember to punch your bore and then shoot 5 round of 5.56mm FMJ to clear your gas tube before you head for home.
These devices are worth the money and the time to get them working. That's my opinion though, others have found these little doo-dads to be frustrating and down right annoying.