Jent has pointed out a very interesting point...where else in the gun world does this appear?...on Barber & Lefever conversions...Greener locks, Greener touch marks, and Birmingham proofs....the era is the same...perhaps Greener reworked some of their own unsalable muzzle loaders...Jerry Swinney told me that when Barber was in business with Lefever, a new Greener muzzle loader cost about what two damascus tubes could be had for, and that's why Lefever specialized in converting them...as for this gun, it's only a possibility, not a guess...notice how ill fitting the locks are to the action...maybe that big trunion represents the remains of a once percussion outside hammer... also updated to hammerless