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Old Jan 09, 2013, 08:59 AM
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United States, MN, Brainerd
Joined Oct 2004
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BP naval gun design

Thanks Tim.
That PDF was for mod of Syren existing guns. Here's a PDF detailing what I think is the simplest and currently best approach to making guns with reloadable barrels.
After building 9 guns with this new approach, here are some observations:
- Make cutting jigs for the small contact pin tubing and cut with razor blade - fast and accurate way to make a lot of pins
- the socket plug holes and the barrel pin holes need to be carefully centered for alignment. A drilling jig and/or drill press should be used.
- the socket tube can be made longer than shown in the drawing, but you don't want it so long that the tubes jam under use conditions (slight dings, dirt, sand, water, corrosion)
- I'm making 40 barrels - 2 sets for 18 guns and 4 extras
- delrin (acetal) is better than polypropylene for the plugs. Polypropylene is sloppy to machine, delrin is excellent. PolyP takes higher temp, but I think delrin will be adequate. Needs to be seen with use. Another option is to cast the plugs in place with thinset mortar or grout, but don't know how to control plug size with that approach.
- crimp and/or glue the plugs pin and grommet ( both in the socket and the barrel) permanently and very securely. They don't need to be removed (even when replacing the igniter assembly) and you don't want them slipping during use. I used CA and crimping to set the plugs and pins.
- make sure the small hole for the loose end of the nichrome wire is well inside the end of the barrel, preferably just inside the point where the wad will be when the barrel is loaded.
- K&S brass tubing is sized for telescoping fit. The socket tube should be one size bigger than the barrel tube. That slip fit, combined with the slip fit of the contact pin tube into the socket grommet, will provide a good friction fit and electrical contact (since these things won't be perfectly concentric)
- lube the barrel rim and pins at contact points with an anti-corrosive grease. I've used a liquid called Bullfrog and also plain old white heat-sink grease (seems to really stop corrosion and is very water resistant)
- make extra barrels and spare/replacement igniters now. Past experience is that these components are "wear items". On tear down of Syren guns, the igniters still were all intact after many uses. But they do burn out at times.
- pre-test each assembled barrel to check for shorts and proper resistance. I get about 4ohms with the wire size I'm using. At nominal 4.8VDC, that should be about a 1.2A current flow, but I measure a surge current of 4+ amps on initial contact. Use high capacity, high C-value batts to handle numerous current draw peaks as guns cycle.
- I'm looking for thermal breakers to add to teh power circuit. With this design and 4-cells (nom 4.8V, max 6V), a gun stuck "on" does get very hot. It's not visible on ship, likely until too late.

That's it. Hope to have a vid this weekend, but weather is still too cold to take Syren (and me) outside.
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Last edited by DanL; Jan 09, 2013 at 09:13 AM.
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