These Caliber Conversions contain all the parts necessary to change your firearm from it's existing caliber down to the inexpensive .22LR rimfire cartridge. The conversion takes less than a minute. It is achieved with no permanent alterations to your firearm. It can be quickly returned to it's original caliber.
Open your gun, pull out the bolt/bolt carrier assembly, slide the unit in, close the gun insert the .22LR magazine, SHOOT .22LR. It's just that easy!
Detailed information - link.