They used to be common to allow pistol cartridges to be used in a rifle (.32 S&W in a .30-'06 for example) but have pretty much gone out of style with the high cost of pistol ammunition.
Adapters that use .22 rimfire in a center fire gun have to be either contain their own RF firing pin or be offset to allow the gun's firing pin to contact the rim of the .22 case. The alternate is to modify the gun, something which is expensive and which many folks don't want to do.
The above refers to chamber adapters, steel inserts that look like a cartridge case and which are usually loaded into and extracted from a chamber like a cartridge.
There is another kind of adapter that we used to call a "chamber jug"; that is a permanent or semi-permanent insert to allow use of a shorter round, like those sold to convert a .30-'06 chamber to 7.62 NATO. These work and are sometimes installed permanently, But proper installation involves roughing the chamber and then using an epoxy to fix the adapter in place. In other words, conversion is one-way. If that is not done, the adapter can come out with an extracted cartridge and the chamber is again oversize. I do not recommend them.
Jim
