6
Specifications for 15mm Launchers (forum.guncadindex.com)
submitted 4 months ago by to c/general@forum.guncadindex.com
6 comments fedilink hide all child comments
 

I've been starting work on a couple 15mm launcher projects but can't seem to find any specifications to help with design. The biggest thing I'm missing at the moment is the twist rate for the rifling. I could technically just use booleans from existing releases but would much rather have some more control over the geometry. Anyone have the specs?

you are viewing a single comment's thread
view the rest of the comments
[–] 2 points 4 months ago (1 child)

I'd think using the CAD from an existing barrel would be the fastest, easiest, and most accurate.

Split the barrel in half longways and measure the distance from one grove to the next.

  • permalink
  • fedilink
  • source
  • hideshow 1 child comment
    •
  • [–] [S] 1 point 4 months ago

    I did end up using CAD to get my measurement, but not quite this way. Had to go back to some secondary school geometry and figured out how to unwrap the helical path. If anyone else wants to do the same process, you need the radius of the cylinder (R), the height of the cylinder (H), and the length of one of the helix edges (L). After a bit of math, you get: p = 2HπR / sqrt(L² − H²)

    For the Pen15mm barrel STEP, this lands less than a thou from a 7 inch pitch (or 177.8mm). Strangely enough, the projectiles from the 15mm Handbook don't match up exactly and give a pitch of 176.04mm. Not sure if there are any implications to this.

    TDLR: The apparent standard for 15mm barrels is a 1:7 inch twist.

  • permalink
  • fedilink
  • source
  • parent