A Haetge /Berlin 16 ga SN 1424 sold by Holts in 2013 and Holts knows the Fürst Pless action but Collath must be mixed into this
"A. HAETGE (BERLIN)
A VERY FINE 16-BORE BERGER PATENT COIL SPRING STRIKER DOUBLE-BARRELLED TESCHNER-COLLATH SLIDE AND TILT 'FURST PLESS GEWEHR' BREECH LOADING SHOTGUN, serial no. 1424,
28 3/4in. nitro reproved bold damascus barrels with bolstered breech ends, raised matt rib with finely inlet carved bone fore-sight, tubes signed 'A. HAETGE. BERLIN. HOF-BUCHSENMACHER' and with a broad band of foliage carved at the breech end, 2 1/2in. chambers, bored approx. 1/2 choke in both, Teschner - Collath patent forward facing underlever-cocking slide and tilt action, recessed bosses with removable striker discs, Berger patent independent coil spring strikers of later centre-fire design (originally developed as needle-fire), set front trigger, finely-figured broad sculpted triggerguard and tang, the action and furniture carved in high relief with bold floral and acanthus scroll motifs, the rear of the plungers with fine starburst designs,13 3/4in. figured pistolgrip stock with cheekpiece, sling swivels, fine fluted edge horn pistolgrip-cap with inset escutcheon with feathered borders and gold-inlaid with the monogram 'WS', engraved steel heel and toe plates, weight 6lb. 12oz."
http://www.invaluable.com/auction-lot/a....00-c-a2b5296ada

and James D.Julia also brings the "Collath type forward lever, slide and tip action" into the description with the 16 ga /24 ga combination gun SN 948

"A. HAETGE, BERLIN 16 GAUGE/ 24 GAUGE COMBINATION NEEDLE-FIRE DOUBLE SHOTGUN WITH DEEP CHISELED ENGRAVING. SN 948. Cal. 16 ga/ 24 ga. Both 26-5/8″ Damascus bbls are smooth bored however top rib is fitted with one standing, one folding rear and front rifle sights. Rear portion of rib is gold inlaid “A. Haetge Berlin”. There are gold band inlays around breech framing relief acanthus scroll engraving. Collath type forward lever, slide and tip action is fitted with short, needle firing mechanism with sliding plungers to compress springs actuating needles. All metal parts except plain steel trigger guard, are engraved with very well cut, full relief, scrolled, large, acanthus leaves with nicely matted background. There is a deep checkered band around standing breech. Forward lever has horn tip. Finely marbled and lightly figured European walnut checkered, round knob, pistol grip buttstock measures 14-1/4″ over steel buttplate, with relief engraved leaf on top, and features swept right hand cheekpiece, and a sling loop on toe-line. Wooden forepiece is checkered. Bbl attaches to forend with screw through loop. Bore diameter: 16 ga left-.661, 24 ga right -.556. Bore restrictions: left -.000, right -.000. Wall thickness: left -.038, right -.045. Drop at heel: approx 2-7/8″, drop at comb: approx 1-3/8″. Weight: 7 lbs. 8 oz. LOP: 14-1/4″. PROVENANCE: Collection of Dr. Geoffrey Sturgess. CONDITION: Very fine. Bbls retain most of their orig Damascus brown, with good definition to pattern. Action appears to have been coin finished, and has darkened considerably, mostly from accumulated oil and grime. Stocks retain most of their orig oil finish, with numerous marks and compressions. Bores are excellent. 4-53070 MGM320 (3,000-5,000) "
http://jamesdjulia.com/item/lot-3159-a-h...ngraving-53070/

very unusual with the 16 ga /24 ga barrels if not James D.Julia forget the 24 ga barrel was rifled it was maybe bore smooth sometimes

A.Haetge sold not allways Fürst Pless guns here is a 16 ga Hammergun
SN 1085