I couldn't get the link to work. I edited the [img] out of the address and it worked:
http://s1275.photobucket.com/albums/timothymanners/?action=view¤t=P1000507.jpgAs far as a percussion conversion one indication is that there is no flaring at the outside of the breech end of the barrels since the original percussion barrels didn't flare since the chamber was the same diameter as the bore. I have a 14 bore Purdey percussion conversion that was converted to a sixteen chamber breech loader intended to use Kynoch thin wall brass hulls. This is because there wasn't wall thickness for a 14 bore chamber. So it is a gun with a 16 bore chamber and a 14 bore bore.
That looks pretty modern (1880s) to me. The big flat one piece sidelock does not look like the lock on a percussion gun I don't think.
The gun you posted called a "bar in wood" gun because the wood wraps around the action.
Best,
Mike