I have an adapter that was designed to shoot a .22 WMR through my .222 Rem. Accuracy was fair, but had some bad luck with the whole darn thing. #1: the adapter (subcaliber device) fit perfectly in my chamber, but is was a real pain to try to get the smaller WMR casing out of the adapter. The WMR casing, upon firing, would get very, very tight in the adapter. I had to remove the adapter and find/carry a stick to eject the spent WMR. #2 Only fired about 100 rounds of WMR through my adapter. I started to have a heck of a hard time with the WMR shells going off. I was set for rimfire, and I know that the firing pin was striking the shell hard enough, but it would take several hits from the firing pin to cause the shell to go off. Sometimes the shell would never go off. This happened with all different types of shells. Finally, I tried to eject the adapter one day, and the rim of the adapter ripped completely off of the back of it. I now have an adapter without a rim, which is completely useless to me. Good thing I didn't spend much on it.
If you are serious about going rimfire, find a rimfire barrel and use it. If you only want to use the rimfire occassionally, a subcaliber device may be a cheaper alternative to buying a barrel. I did have decent accuracy...when it did work. Overall, I give them two thumbs down.