Idea, for creating a rifled barrel, the easier way (as I imagine it):
1) Start with thin sheet of styrene, and eventually place that curved, and inside a hollow plastic barrel.
2) Add rifling, using thin styrene strips on a FLAT piece of thin styrene sheet
3) Place the customized sheet of styrene inside a hollow barrel, and create slight twirl.
4) Glue in place along that one seam, the whole way down through the barrel, and maybe glue on front/end as well..
5) Then.. saw the barrel to length and clean up.
Accurate placement of strips of styrene can be made, by filling the width of the sheet styrene with strips, glue on every other one, then remove the "spacers" to "create" the rifled grooves.
Does this sound like a plan or not?
This way, one can also get to paint the inside rifling, with a metallic color before placing it inside a cylinder!
Uuh, perhaps another way to create rifling, could be to scribe into plastic, but perhaps very very tricky to get proper parallel lines, ofc, slight errors might be unnoticable, practically speaking.
The Dora gun barrel has 96 + 96 grooves iirc. 96 top fins, and 96 grooves.
Hm, in order to get proper shape to the grooves, I could very gently sand the grooves with some tool, to avoid the "fins"/"grooves" being simply square shaped in cross section.