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Specifications for 15mm Launchers (forum.guncadindex.com)
submitted 4 months ago by to c/general@forum.guncadindex.com
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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?

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[–] 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.

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  • [–] [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.

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    • [–] 2 points 4 months ago (2 children)

    Take a rifled chalk/whistle round insert it into the barrel just enough to begin engagement with the rifling mark the round at it's 12 o clock position best you can. Push it far enough to rotate the mark a full 360 degrees the distance it took to get that full rotation is your twist rates number written "one in (whatever number you came up with)"

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  • [–] [S] 1 point 4 months ago (1 child)

    I was going to attempt this method of measurement but figured it would be too inaccurate. However, I'd be satisfied rounding to the nearest half inch if someone could confirm the design uses an inch-based twist rate rather than a metric pitch.

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  • [–] 1 point 4 months ago

    Tbh if I were you I'd make a projectile specific to the barrel you end up with using boolean cuts to eliminate the headache of recreating pre-existing stuff. Or you could always just use the existing screw on 15 barrels originally used on the pen15

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    • [–] 2 points 4 weeks ago

    the captain America was 1:7 and there is a mandrel to use for making your own barrels in one of the releases, if you can't find it DM me and ill send it to you.

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