I have an old 12 gauge double barrel shot gun with damascus barrels. Would it be safe to shoot this old gun with 20 gauge barrel inserts or tubes? I would really like to use the gun instead of dedicating it to be a wall hanger. What do you think?
It might, but the age and design (as well as the quality of manufacture) are also factors. Old guns are often not made of materials equal to more modern ones, and have usually been stressed by long use and/or worn or damaged by neglect, poor maintenance, or just plain old age. Then, too, a 12 ga. double with liners would be a heavier and less 'handy' arm for any use, than a gun originally made for the smaller gauge.
Many owners of damascus or other pattern-welded barreled shotguns do still shoot them, some with 'light' smokeless loads and some with black or black substitute powders, but the bottom line is that there can be no certain safety margin in shooting a gun with a very old barrel or barrels which are a mass of welds, usually of dissimilar metals, from end-to-end, and no way to be sure of the actual integrity of that assembly at this late date.
Caution is best, but, whatever you do, if you decide to shoot your double, have it inspected very thoroughly by a competent gunsmith, and a second or more opinions is a good idea, as well.
PRD1 - mhb - MIke
IF it proves safe to use (by a competent gunsmith) then Vintager loads from RST would be a good choice to useAssuming the gun is sound you will probably want nitro for BP loads. So called "lite" loads do not neccesarily run any lower pressure than full house loads. A nitro for BP load will be specifically loaded to BP pressures for old guns. Or you can go retro and shoot actual BP loads. There are such things as twist steel barrels for nitro loads but most were meant for BP loads. The last twist steel gun I know of was a Holland and Holland made for modern nitro loads, if I rember right it was made circa 1983.