The two Hollenbeck guns on GB have been re-chambered to modern cartridges and are apparently over-priced as they've been listed for about two years. These guns were mostly chambered in obsolete BP cartridges (25/20 and 25/25 Stevens, 32/20, 32/40, etc.) Some later examples were chambered in 25/35, 30/30, and 32 Win Special; but I know of no chamberings larger than .32 caliber. I own a Three Barrel Gun Co/Hollenbeck drilling in 12/12x32-40; the original records for this gun still exists and it has survived intact and unaltered. I got this gun from Cherry's and it was advertised as non-working and priced accordingly. After they'd listed the gun for months, I made a low-ball offer which was accepted (all those guns are on consignment). I wanted the gun because it is part of the Hollenbeck/Syracuse Arms/Baltimore Arms/Hollenbeck Gun Co story that I have researched for years and I needed a cheap representative piece for study. Externally this gun was in great condition and I figured, should I later part it out, the price paid was less than the value of the parts. When the gun was received it was disassembled and the problems quickly revealed; the cocking arm was broken off the right side hammer/firing pin unit, and the cocking "ear" was missing from the left side of the rotary cocking device housed within the barrel lug. Lo and behold I see an eBay listing for a parted out Royal Gun Co drilling the very next week that some knucklehead had re-chambered to a high pressure cartridge and blew the lug off the barrels. I was the only bidder on the lug and internal parts; Buck Hamlin was able to fit those salvaged parts into my gun and I now have a functioning TBG gun. As you are an advanced machinist/gun nut, then I encourage you to check out Cherry's for a cheap project drilling should that be something you want. My experience is that it's much more cost effective to begin a restoration project beginning with a gun that still retains most or all of its parts.