are any of the 22 lr dedicated upper receivers able to be put on a full auto lower ? my friend has one and I was thinking how much fun it would be . And not so costly .
I can't speak for the price being "not so costly", but if you want reliable full auto, it's not likely going to be.
Keystone Accuracy in Pennsylvania has what you need. Guy's name is John Scandale, and I'd say he's ranked in the top 5 accuracy AR smiths in the country at this point. His .22 Uppers are dead reliable, including full auto rating.
I believe cmmg makes full auto sear trips to be used in their 22 conversion bolt. So you could use any upper you already have with one of those. Or one of their 22 dedicated uppers.
I have a couple of dedicated Chiappa .22lr uppers. Never had a problem with them or the magazines in semi but never tried them in any other modes. If you would want to try one of them let me know. I'm always up to test stuff!
Dan
The CMMG uppers seem to be pretty reliable for me, with the full auto sear trip installed, as long as I'm using decently zippy high velocity ammo (Mini-mags, Remington Thunderbolt, Winchester Super-X, CCI AR Tactical, etc). Federal Automatch and Rem Golden Bullets don't work very well in it (though, I've generally found that to be true for a lot of different guns with those two rounds).