I picked up an 8ga SxS Evans hammer gun with 35.5" London Fine Twist Damascus barrels. I've shot a lot of game with it this year (grouse, phesant, etc - but of course, not any waterfowl ) and love to shoot the 127yr old beauty. The only problem is that the local ranges I can get to on any bit of a regular basis only allow 12ga and smaller (not even my 10ga) with a maximum 3.25 dram equivalent load. Also, loading shells is a 'one at a time' process with hand tools which takes a long time. Fine for hunting, but not so fine for plinking. For this I've found a solution.

I contacted a gentleman that makes chamber adapters and have ordered a pair of 8ga-12ga adapters. I'm planning on getting them in 3.5" chamberings and 18" or longer, just in case . This will allow me to shoot practice at the local ranges and possibly take her out for some waterfowl, the original purpose of this 14lb gun.

My question is this:

1) Will the pressures of a 12ga shell (9-13,000psi) push the barrels 'off face'? I wouldn't think so because it is built like a 'spit' house and has a dolls head on top.

2) Are there any other problems you see with my solution besides increased weight?

Thanks,
BMG

BMG,I'm no expert by any means, but I have always been taught not to fire smokless in Damasscus bbl'ed guns

BMG:
One way of guesstimating whether the gun will be able to cope with the pressure is by working out the total (theoretical) back-thrust on the breech.

A 12-bore cartridge has a head diameter of .810 inches, which equates to a surface area of .516 sq inches. For a 10,000 psi cartridge, this results in 5,160 lbs of back-thrust on the breech. Doing the maths, using an 8-bore cartridge head diameter of .925 inch (area of .672 sq inches), we would get the same backthrust from an 8-bore cartridge which generated 7,680 psi. Do you think the gun was built to handle that pressure? Hopefully someone here may know the actual proof and service pressures for the 8-bore BP shotgun, I'm afraid I don't!

I must stress that this is only a guide, there are a number of other factors which may influence how much of the peak pressure actually translates to back-thrust force on the breech.

Also, there are any number of 12-bore shotshells which produce a much lower peak pressure than 10,000 psi. I would be looking closely at that option.

BTW, the idea of chamber inserts (as opposed to the barrel inserts you plan to acquire) is to allow the wad column to expand into the larger bore as it exits the chamber, thus dropping the pressure. Typically 16-bore inserts for a 12-bore, or 20-bore inserts for a 16-bore. However, dropping from 12-bore to 8-bore and still maintaining a gas-seal would be a very big ask of the average plastic wad!

Good luck with the project, sounds like a very interesting 'proper' fowling piece!

One other point is that you should NOT use steel shot in a Damascus Barelled gun. That would end the waterfowl loads which would probably be your stoutest ones.

Guess you with have to use bismuth or hevi-shot. Can you use those with Damascus bbls?

Thanks to all the posters with replys. I should have put in some more info as to my knowlege of Damascus barrels.
1) I know of the 'default' response not to use smokeless in them, however, there are many fine damascus guns that can handle the pressures just fine and are nitro-proofed. Early on in the BP->Smokeless era, guns were blown up due to HEAVY corrosion from BP, weak/lightweight steel (there are BPE rifles that function quite well with significantly higher pressures than shotgun shells), and over pressured smokeless loads (hence the dram equivalent).
2) I realize that I cannot use steel or even worse Hevi-shot in damascus barrels. Having said this, the liner is steel and can handle any shot I can put through it. I am looking into the option of a longer liner than 18" to further contain the shot column for the express use of Hevi-shot on waterfowl.

My only concern is relating to the backthrust on the breech face.
1)I dont know what the original backthrust for 8ga BP loads was
2) if the use of 9-10,000psi 12ga loads with liners will be more
3) and if so, would it push the barrels off face.
4) Anything I should do, look out for, or misc info.
5) Any idea as to how much weight an 18" liner will add? 30"?

Thanks,
BMG

I think it's a bad idea and you should box it up and send it to me right away.

Maybe you could pickup a couple of Mossberg 835 ultimag bbls and modify them to use as liners. I think the 835 opens up to a 10ga bore after the chamber so you would have to check to see if barrels could be turned down enough to fit the 8bore. Maybe just use a stright 12ga. If you could keep a screw in choke in the liners and use a full choke, would that keep the shot pattern close enough to not harm the damascus bbls? Maybe make the inserts about 1 or 2" short of full length.
I'm thinking that the new steel liners should handle the pressure of a modern load just fine. I've looked for but haven't seen any pressure data for black powder shotgun loads. If anyone knows of a sight, please send it to me. I'm thinking that with the doll's head as a third fastener then it should handle the bolt thrust of any 12ga shell. The book I've been reading says that the actions are much stronger and the limiting strength was in the barrels.

Of course I have no experience here and just talking out of my half full, or was that empty, cup of coffe. If it was my gun, I would do it.