Anyone here have an idea when the British shotgun maker Wm. Moore might have started using back-action locks on his 10-11 bore percussion doubles with Fine London Twist barrels?

Rebounding or not?

First off, this is not for dispute, but info. Did anyone ever fit a rebounding lock to a percussion (ML'r) gun, can't recall ever seeing reference to one. The hammer would still need to be drawn to full cock for capping anyway, so would seem to not be an important factor for them. I do realize of course a "Cartridge Gun" is fired by percussion to its primer but the term "percussion doubles" to me just means a ML'r fired by percussion caps. The rebounding lock was, IMO, a great development for the breech loading hammer gun.

Wouldn't a rebounding hammer be unsafe on a percussion shotgun, as you want the weight of the hammer and spring sealing the nipple and cap at the instant of peak pressure?

Yep sure would, unless you wanted your hat blown off.

No body ever said I could read for speed and content at the same time!!! Silly question in light of the ML connection!!

This should have been rather obvious & I totally let it slip right past me. By a similar token rebounding hammers are I believe generally considered undesirable on high intensity cartridge guns, as a Dbl Rifle. In this case a pierced priker is much more apt to occur if the firing pin doesn't remain in the primer under pressure. The use of a rebounding hammer is mostly confined to breech loading shotguns, or a few low pressure rifles.

This may be of no help, but it is what I can offer. Wm. Moore & Grey S/N 2752 has rebounding hammers. Moore & Woodward S/N 2978 (could be around 1874) is noted as a JUL bar action pinfire converted from percussion; no mention of rebounding locks. After 1850, Moore should have been marking guns Moore & Woodward.