shock pump stroke volume?

[32103940]

im looking to make a 300psi singleshot gun powered manually by shock pump. my aim is higher pressure, since my last project was bicycle pump-powered at 140psi, and i understand im going to have to pay attention to chamber volume this time since shock pumps have tiny stroke volume.

my question is...how tiny? i dont even have a ballpark figure so i cant do any rough calculations on how many pumps to expect for a given chamber size. my barrel is 7.4mm ID and 60cm long...or about 7/8 fl oz in imperial, so i wouldnt need a large chamber. in fact the dead volume in the qev, T-piece, elbow, safety blowgun(pilot) combined are non-negligible and might make it more possible for me to make a tiny chamber.

and speaking of safety blowguns, i understand they can be pushed much further past the rated 130psi. any first hand upper limits in practice?

[jackssmirkingrevenge]

With a good shock pump, you can take a 1 cubic inch chamber to 300 psi in less than half a minute, anything bigger is pushing it in terms of pumping effort. That would give you less than 1:1 chamber:barrel ratio but definitely enough for very good performance.

and speaking of safety blowguns, i understand they can be pushed much further past the rated 130psi. any first hand upper limits in practice?

In my experience withthis type they are good to 450 psi or so, beyond that they start to leak

[32103940]

thanks much.

another question please. what size is the female thread on a paintball tank (pin valve fitting removed)?

[mark.f]

5/8"-18tpi UNF.

[Gun Freak]

They are very strange threads, not something you can find in a hardware store. Myth has it that it's close to 3/8" NPT...

[mark.f]

Actually, you can find a fitting in most hardware stores. A 3/8" SAE flare fitting uses 5/8"-18 threads.

However, not many commercially available fittings will have the thread engagement required for higher operating pressures. For that you will have to use adapters and valves purpose made for CO₂/HPA cylinders or machine your own.

[Gun Freak]

I meant you can't find the exact thread in a hardware store...

[mark.f]

Are you talking about threaded studs, bolts, etc? It's a fine thread, whereas most hardware stores sell 5/8"-11 coarse threaded fasteners.

The 3/8" SAE flare fitting uses the exact same threads as the neck of a paintball cylinder does, they are simply shorter in length than the ones on a pin valve.

[Gun Freak]

Ah, good to know. Thanks mark. I was just going by what I'd read on previous threads where people asked the same question.

[32103940]

Ah, I was hoping to use a paintball tank directly into standard npt or bsp. Is it easier to work with the cga 320 output instead? Like cga to npt adapter...

[jackssmirkingrevenge]

if you keep the pin valve fitting it's compatible with <s>3/4"</s> 1/2" BSP.

edited for facts.

[32103940]

but i'd need some way to keep the pin depressed, or maybe remove the pin...is the tank valve easy to disassemble?

[jackssmirkingrevenge]

Removing the tank valve is simply a matter of unscrewing it. As to the pin, I don't know how it's attached but it should be fairly easy to remove, if not - heck, drill it out

[32103940]

haha yeah. i dug around the archives and i saw a post by you with an attached pic of a co2 tank screwed directly into a 1/2" bsp inline ball valve...

[jackssmirkingrevenge]

http://www.spudfiles.com/forums/viewtop ... tml#278506



Ooops, I said 3/4" BSP in the previous post, edited.