Holt's have a muzzle loader in the next auction https://www.holtsauctioneers.com/asp/ful...888&image=5

"A CASED 20-BORE DOUBLE-BARRELLED PERCUSSION HOWDAH PISTOL SIGNED COGSWELL, LONDON, no visible serial number,
circa 1865, with browned laminated 7in. London proved barrels, the top-rib signed 'COGSWELL 224 STRAND LONDON' (bottom loop detached but present), colour hardened breech-blocks with nickel plugs and gold line and engraving to the rib-end, bead fore-sight, borderline and scroll engraved colour hardened top-tang, curved border and scroll engraved colour hardened back action locks signed 'COGSWELL', both hammers refinished with repaired spurs, walnut full-stock with chequered swept grip, colour hardened butt-cap with central trap, blued trigger guard and captive iron ramrod, the whole retaining much original finish and colour except where noted and in its maker's oak storage case, lined and compartmented in green baize, yellow Cogswell paper trade label and a near full suite of original accessories except mould (absent), the case also in fine condition "