Firearm with interchangeable barrels and ammunition cylinders

In a firearm of the type having a frame for mounting a multiple chamber ammunition cylinder, said frame having a rear sight mounted thereon, and a threaded frame bore for removably mounting a barrel, a plurality of said ammunition cylinders with each of said cylinders being adapted for use with a different caliber ammunition, means for selectively mounting any one of said plurality of cylinders for revolution on said frame, a plurality of barrels, each said barrel having a different diameter barrel bore therethrough corresponding to a different caliber of ammunition associated with one of said plurality of cylinders, each barrel having a thread engageable in said frame bore and located at one end of said barrel for allowing selective mounting of each said barrel in said frame bore, longitudinal barrel extension means located on said one end of each respective barrel and being operative when said respective barrel is fully threadedly engaged in said frame bore for interfering with the mounting and revolution of any said cylinder in said frame which cylinder corresponds to a caliber of ammunition larger than the caliber of the barrel bore of said respective barrel, an improvement which comprises a plurality of interacting safety features including a barrel alignment mark located adjacent each said barrel thread on each of said barrels, a frame alignment mark located on said frame for alignment with said barrel alignment marks when each said barrel is fully threadedly engaged in said threaded frame bore to insure full threaded engagement and thereby the operativeness of each said extension means, and a forward sight mounted at the other end of each of said barrels and being operatively oriented with respect to said rear sight for allowing the aiming of said firearm when each respective barrel is fully threadedly engaged in said frame bore, the orientation of each said forward sight thereby also insuring the full threaded engagement of its respective barrel and the operativeness of said extension means.