If you saw something like that, then it was something which somebody custom made on their own. No such product is manufactured for public sale, and it would have no practicality even if it were. What you saw on YouTube was probably a creation of someone with too much time on their hands, and access either to a welder or a supply of JB Weld which they couldn't find any better use for.
Actually, No. Check out these famous gunmakers.
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The Stevens 311 is a double barrel shotgun.
You will have to provide a detailed description of the action, ALL markings, barrel length, rifle caliber and finish.
barrel, stock, action.
Barrel, action, stock
Stock, action, barrel
Requires hand on inspection.
You will need a professional appraisal
Probably a one of.
Yes there are many fine double rifles out there, they do tend to be pricey.
That would depend on the caliber, and type of bullet, the rifle uses.
Condition?
Should be on the barrel near the receiver.