Who makes a drop in .22 conversion for an AR that is compatible with full auto guns?

Here are two Spikes and Ciener

I cannot (and will not) recommend either one because I have not tested them, and I have requested information from both and the both did not respond.

but others have used them.

I (and several of my buddies) have the CMMG unit which runs flawlessly in semi; I have heard from others that it works just fine in auto but can't verify it personally. I did find the following description which may be of help:

CMMG .22 Conversion for AR15 Firearms. The CMMG .22 LR caliber conversion is a .22LR caliber rim-fire device which replaces the standard bolt/bolt carrier assembly in the AR15 family of firearms. It allows the use of inexpensive .22LR ammunition in place of 5.56 (.223 Rem.) It is a blow back operated sub-caliber conversion device that allows semi-automatic firing of the .22LR high velocity cartridge in the AR15 & M16 rifle. The same unit with the addition of automatic trip and anti-bounce weight (M16 unit only) allows select fire (semi and auto) firing of the .22LR high velocity cartridge in the M16.


Don't hold your breath waiting to hear from Ciener. Customer Service isn't exactly his forte; Brownells dropped his product in part because of the unreliability of his support and product supply. I understand that the Spike's unit was just a modified Ciener.

I think the Atchisson/Ciener are the same with CMMG, Model 1 Sales, Spikes Tactical, Tactical Solutions, and Target Master all very close with a few slight changes.

I actually used to use the M261 Army Unit, and I think Olympic arms now makes that one. (I don't think I would get the Oly unit)

Just make sure you buy one that will allow you to use Black Dog drums and mags.

Good point about the mags. The CMMG does use the BDM's, which is a bonus for me since my SIG 522 uses them as well. 

I am going to try the spikes full auto and I will report back.

I've run the Ceiner with good results for several years now.  His customer service/customer response is certainly not his strong point but the unit has been reliable, including with BDM mags.