Abstract: This relates to an inexpensive conversion kit for handguns wherein inexpensive small caliber shells may be fired from a large caliber handgun. The kit includes a special adapter shell which is formed of two separable housing members into which there is inserted a small caliber shell, for example a .22 caliber shell. This shell will generally be of the rim firing type, whereas the larger caliber shell of the handgun is normally of the center firing type. Accordingly, the adapter shell will also include a special rim firing, firing pin which will be activated by the conventional firing pin of the handgun. The kit further includes a special barrel which is readily mounted in the handgun as a replacement barrel and which has a breech for receiving only the adapter shell. The converted handgun will operate in the normal manner.