Leverlover Colt SAA

It's a 1912, first generation Colt. Since it has the correct Colt Revolver rifling and no markings, they were undoubtedly buffed out in preparation for the nickeling.
A factory letter will tell you the original caliber, barrel length and finish.
After WW2 and before Colt resumed manufacture of the SAA (2nd Gen.), Colt and others rebarrelled and recylindered many "obsolete" calibered SAAs to 38 Special. Subsequent owners as myself had them reconverted back to their original calibers.