Peter:

Yes, it would be nice to find an action to fit those barrels to. Having new double rifle barrels made is expensive as hell. The problem will be finding an action to fit them to.

I had seen those barrels in the catalogue. They're from a double rifle that was only retailed by Atkin, built for them by someone else. It was almost certainly a boxlock. Note the Birmingham proof marks. Also note the non-matching trade maker's number on the key rib between the barrels. Atkin's number 3065, trade maker's number 87,933. Also note the doll's head extension. There is very little chance that these barrels will fit an Atkin sidelock shotgun, especially if it is a best, which will have no doll's head extension.

It would be a good idea to find out who the trade maker was. Looking at them, I can't tell. The Atkin number is from 1931 according to published SN tables. However, the proof marks are 1904 rule (no case length mark) which were superseded by new rules in 1925, which added the case length mark (it would say 3" on the flats). The table could be wrong, but the gun may also have laid around for a while. It would be a good idea to contact Ken Duglan at Atkin Grant & Lang to see what Atkin's records say. The records that survive of many of the London firms (day books) generally don't indicate the source of a bought in gun, or even that it was bought in. The availability of that information depends on what records survive.

Still, they're probably worth what you paid for them.