The only variable power scopes I know of that will mount forward of the hammer are those short scopes with a 20mm objective diameter, Leupold and other make 1-4x20, Weaver used to make a 1-3x20 V3. There are several fixed 2½x and 4x scopes that work fine too, all of these require a long mount like the obsolete H&R Ultra rail, EGW or a modified Weaver #82, all shown in the FAQs.
Tim