The .22lr AR Conversion Kit from CMMG is the easiest to use .22 conversion that we have tested for the AR platform. It is easy to install and remove, and is compatible with a wide range of ARs. The kit consists of a replacement bolt assembly that pairs a rimfire bolt and associated spring with a sleeve that fits into the chamber and allows .22lr ammunition to be fired in place of .223 or 5.56. Special .22lr magazines are required, and are available in 10 and 25 round versions.
The assembly is constructed from stainless steel, with the spring guide welded to the bolt. The weld is well done and without external flaws. Considering the low pressures of .22lr ammunition, the weld is unlikely to fail even after long term use. Over the course of our testing, we recorded no wear to the product beyond minor cosmetic blemishing and scratches consistent with use. Fouling and build up also depended on the ammunition used, but did not have an effect on function until it became excessive. With proper cleaning and care malfunctions due to fouling should rarely if ever be a problem.
CMMG states that 36gr plated nose rounds work best with the conversion kit, and we found that this is generally a good place to start. Depending on the firearm that we installed it in, accuracy varied greatly. None of the different makes of ammunition that we used produced tight groups, making the kit a great fit for people looking for affordable trigger time and training, but less so for hunters or target shooters. Point of impact was consistently 2-4″ low, but could be sighted in properly if the intent were to keep the gun configured as a .22lr.
The magazines fit somewhat loosely in all of the firearms that we tested them with. In some cases, we did experience feeding issues when applying pressure to the magazine (using it as a rest, which is generally not a great idea anyway). The magazines that came with the kit worked well, but there have been reports of after market options being less reliable.
MSRP is $279 for the kit, which includes the bolt, a replacement charging handle, an adapter for the forward assist, and one 25 round magazine.