The markings on the left side of the breech are the proof marks of the Company of Gunmakers in London. The markings are actually a Crown/GP (for Gunmakers Proof), then the Crown/V (view mark), then a "lion rampant" over a script G (the Provisional Proof). On some London barrels, the 25-bore gauge mark appears in the proofs, on others it was stamped on the bottom of the barrel.

J.JONES was likely either the stock maker, or more probably, the gunstocker. He could also have been one of Barnett's inspectors. However, it is possible that this is the name of a salesman who dealt in volume sales, to purchasers either North, South, British Volunteers, or private sales. I don't have my references here to check this name.

Hope this helps,

Geoff