I made the original DeSteiner M1887 2 years ago, and recently I revisited it, so why not making a variant with stock and a long barrel?
I combined barrel-tube part 2 and 3 so that I don't have to assemble them and to reduce connection seals. It's 342mm tall, so you need a larger print volume to print it.
You need to glue the extended barrel top on the main barrel, just simple as that.
I used the stock that you can find from the remix of DeSteiner M1887.
The author remixed this model.