SpudFiles

this gun has spare valve parts from previous guns but new pipe. it is a redesigned model of this:

now it is safer and in my opinion, much cooler looking.
this is my current ammo

i posted a topic here
http://www.spudfiles.com/forums/viewtop ... tml#105256
Specs:
-2'' chamber
-1/2'' barrel 27'' long
-1'' inch modded sprinkler valve
-it has a sort of coupling that fits over the muzzle and holds a thin plastic sheet, which keeps water out the the barrel before the spear is shot
pics:

There might be significant accuracy decrease when the ammo exits the barrel due to the crazy physics of air/water interfaces.

Tthats why normal spear guns use springs.

wow, cool orange blowgun. 100 times better than the last one.

That's cool, it's the first underwater gun I've ever seen.

Well I think most pneumatics could technically work underwater, if you think about it. i mean the concept of a pneumatic gun requires that it be airtight. I will say, however, this is the first gun I've seen made specifically to be used underwater. And since you're using it in water, your projectile will actually be called a harpoon.

EDIT: If you are going to be holding it underwater, you might want to let the barrel fill with water, then load the projectile. Then the effect of the air/water interface should be negligible

yes but then it increases the mass of my projectile by about 100 times since i have to shoot all the water out too

Well it wouldn't be by 100, but it would be considerably heavier. If you don't want to do that, then I would cover the end in cellophane or something, because if the barrel fills partially with water, then it'll really throw it off. And since you're using that harpoon underwater, I would suggest adding something at the back there to bevel the plastic cap. If that's flat, it'll drag a lot, but if you were to put something on it, say a cone made of soda bottle plastic or something, your harpoon would be much more aeordynamic, er, water...o...dynamic? It would swim better...

Make the dart hollow and then sleeve it on the barrel.

That way you can fire it without messing about with plastic and don't have the problem of it suddenly hitting water.

Michael

yeah i do have a cover for the barrel, i mentioned it in my initial post, i am also just about to put cones on the darts, ha, great minds think alike. btw, i think its hydrodynamics.

they i would have to completely redesign the gun and ammo

No make the spear the cover.

Hydrodynamics isn't to do with an projectile going from a less dense medium to a more dense medium.

Michael

no the force of water are hydrodynamics, while the forces of air are aerodynamics.

No....hydrodynamics is the study of a moving liquid as opposed to hydrostatics - where the liquid is stationary. We're talking about the change from a less dense to a more dense medium by the spear and as I said that isn't hydrodynamics.

You wouldn't need to redesign the gun just the ammo.....

Michael

you can use a condom to cover the barrel but you really can there are condoms for guns for under water purposes

what i have is work and it cheap, thats 3tables. i have heard of those before though

why not use sharpened 1/2 inch wodden or even 1/2 steel rod. it would seal your barrel and dont forget to grease it for less friction.