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16 ga hammer gun SN 27755 with 1 1/2" rifled chamber insert for the 40 mm long 16 ga bullet cartridge right and lefts side. no doubt had also smooth inserts once but this is lost somewhere.
http://jamesdjulia.com/item/lot-3160-dreyse-16-gauge-double-combination-rifle-shotgun-53102/

"DREYSE 16 GAUGE DOUBLE COMBINATION RIFLE/SHOTGUN. SN 27755. Cal. 16 ga 1-1/2″ Chambers. 30-1/4″ Steel bbls are marked “F. v. DREYSE” and “SOMMERDA.” as well as “PATENT”, on full length flat rib, fitted with folding U-notch rear sight, and German silver barleycorn front. Bbls are fitted with unusual semi-permanent inserts with short chambers having forward section rifled for approx 2″ with four extremely deep lands (Consignor states “Per Dreyse patent” see also the patent model for this leed rifling design elsewhere in this catalog). Remainder of bbls are smooth. This appears to be a variation on the Paradox system to combine capability of using ball and shot in the same firearm. Inserts have integral ears that project beyond sides of bbls to allow removal and exchange for unrifled shot chambers (not included). Round bodied, forward lever action is fitted with peninsula rebounding back action locks with serpentine hammers. Action and locks are engraved with geometric borders. Both triggers are set. Steel trigger guard has carved horn grip extension. Well-marbled European walnut buttstock measures 14-1/8″ over steel buttplate engraved with SN. Bbls attach to captive forend with pivoting lever at front of forend. Bore diameter: left-.657, right -.658. Bore restrictions: left -.000, right -.000. Wall thickness: left -.042, right -.040. Drop at heel: approx 2-1/4″, drop at comb: approx 1-1/2″. Weight: 7 lbs. 7 oz. LOP: 14-1/8″. PROVENANCE: Collection of Dr. Geoffrey Sturgess. CONDITION: Fine. Bbls retain most of their orig blue, with considerable freckling on left side, thinning overall, with numerous marks and light scratches. There is a slight dent 11″ back from muzzle on side of left bbl. Action and lockplates retain 30 – 40% orig case hardening color with evidence of some cleaning. Stocks retain most of their orig oil finish with numerous marks and scratches, some fairly deep. Bores are excellent. Action is tight. Locks are crisp. Action screw replaced. "