Bring it to a legit gunsmith and let them do a full rundown/rework on it. They'll make sure it's safe to fire and get it properly working. Do not try and do this on your own. A proper gunsmith will be able to check for microcracks and any delamination of the metals. You don't want a break action to blow up in your face.
guns
Keep it civil.
No advice, but that’s a pretty dope gun
I personally would NOT fire smokeless in that gun. Sure, some guys proved THEIR barrels didn't explode, but not all laminated steel or damascus barrels are all the same. On top of that, age is a factor on older guns too. Is the barrel pitted or cracked? These barrels are not proofed at all for smokeless.
Honestly, just buy 12GA ammo off the shelf, the cheapest you can find. Cut the top off, dump the wad, shot, powder out. Then put black powder (777 or whatever substitute you want to use), wad, shot, wad, and then use tallow or bees wax and pour it over the top, not letting it drop off the sides.
I can't find the video of Berry showing "cut shells" on Iraqveteran8888 channel atm, but there are other sources.
R u a cowboy?