making speargun bands question

hey folks, can someone tell me an equation to use to determine the length of speargun bands for a gun?

i thought it was something like 1/3 of the pull length but who knows: )

any tips appreciated!

john

John,here's a generic guide.I've used 2x-3x depending on rubber.Some recommend a pre-stretch of 300% for an hour then use about 2.5x length.(green rubber)The rubber will stay stretched out a little.
  http://www.homepages.paradise.net.nz/quentinl/bulk_rubber.htm

hey folks, can someone tell me an equation to use to determine the length of speargun bands for a gun?

i thought it was something like 1/3 of the pull length but who knows: )

any tips appreciated!

john

Based on what I've read, you're using a 48" 5/16" shaft & 5/8" bands?

With any multi-band configuration, there's a trade-off between power and accuracy.  Which is your priority?


I usually do the following:
Take distance between band-slot & pin that the wishbone goes to.
Divide in half and add 2 inches.  I like my bands really tight, so if you want a little longer bands, adding 4 inches may be better.  You can always shorten your bands, but not the other way around.   

That being said, 3 5/8" bands are a lot for that setup.  JBL woodies are not known for their trigger/housing strength.  It's a bit late, but I think your setup would work a lot better with a 9/32" shaft & 2 5/8 bands.  That's easy enough to modify at a later date.


Looks like a cool project, good luck with it.   

thanks guys! what a wealth of knowledge. i will go with your guys' advice and see how it all works out. with my 5/16th shafts i only have 2 notches for wishbones so i will be using just 2 5/8 bands for now. someone said i could machine in another slot but i'll try it this way first.

that JBL trigger mechanism is ok for now but i also heard they can be overloaded to the point they wont fire. just to be safe i'll try to err on the more forgiving lengths with the bands: )

thanks guys, i'll let you know how it all wraps up. maybe go out this weekend and give it a whirl in monterey.

john

Fuzz is the mac-daddy spearo.He's got the tecnical info.