Hand Pumpability.. And First post :)

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Hi all..
As usual I'v been lurking for the last week or so, cramming my brain with as much info as possible.. And I'm gonna build a semi-auto 6mm gun based on JSK's spring/rubber band powered breech. I'm pretty nifty when it comes to making things so the build process and all should be fine... but here comes my question
being a poor uni student, unfortunately I dont have an air compressor.. now I know everyone just sighed and glanced at the search button, but believe me I'v searched. So here is what I would like to do, I would like to run a low volume chamber at "high" pressure (say 100-150psi). When I say low volume I mean about 5cm diameter by about 20cm long (yes I am Australian and work in cm's )
Ideally I would like to run a permanent hand pump setup, I dont mind if it needs a few pumps between shots, so long as its completely portable. So here's my questions:

a) Is there any way I will be able to get a smallish chamber to that pressure with a hand pump? Maybe a shock pump?

b) Will a pvc chamber sealed with a buttload of epoxy hold that kind of pressure?

c) Am I likely to get more that a single shot off between pumps?

I'll be running it off a blowgun handle/trigger setup.. bunnings have some pretty blue and red annodized ones for about $15 8)
I thhiiinnnkkk thats all the info you should need.. I plan on doing a write up with pics,vids,damage etc etc etc once the ball gets rolling and I get out of this damn hospital bed (clinical drug trials gotta fund my hobbies somehow).
But anyways, thanks in advance and I'm hoping you all dont slap the s*** out of me for asking potentially silly questions

cheers,
matt

[jackssmirkingrevenge]

But anyways, thanks in advance and I'm hoping you all dont slap the s*** out of me for asking potentially silly questions

Anyone willing to potentially compromise their health in order to fund a hobby can ask all the silly questions he wants

a) Is there any way I will be able to get a smallish chamber to that pressure with a hand pump? Maybe a shock pump?

A shock pump will take forever, have a look on eBay - there are plenty of pumps that will take you past 200 psi more comfortably that won't break the bank, otherwise there are several members who have built their own pumps successfully, Gippeto also has a tutotial posted.

b) Will a pvc chamber sealed with a buttload of epoxy hold that kind of pressure?

I don't know about JSK but JSR has plenty of prototypes that do, with good design it doesn't need to be a buttload either

c) Am I likely to get more that a single shot off between pumps?

With such a relatively small chamber, I wouldn't say you'd get more than 2 useable shots.

And I'm gonna build a semi-auto 6mm gun based on JSK's spring/rubber band powered breech.

Which one exactly? The blow-back one hasn't worked too well so far at low pressure.

Since you're limited for air capacity so efficiency is paramount, I would go for a valveless/popoff setup

[Insomniac]

Not sure on a hand pump, but a shock pump will not work... It'll take FOREVER to get it to pressure.

And with PVC, use PVC cement. Not epoxy. Not even if JSR asks you nicely.

EDIT: HA! I wrote this without seeing JSR's post! I'm sorry, but now you're just getting predictable!

[Crna Legija]

if you go to a bike store you will defiantly be able to find a pump that can get to 150 check ebay aswell, don't get a shock pump because you will be pumping for a hour.

you can get pressure rated pvc pipe and end caps at reece plumbing, so you don't need any epoxy.

idk which one of JSRs creations you wanna replicate but you should be able to get at lest 2 shot off, but at 6mm they will be very week, id sagest using a blow gun as you main valve and getting a cap gun to hit the valve stem as hammer.

and welcome
what state you in if you dont mind me asking

[jackssmirkingrevenge]

And with PVC, use PVC cement. Not epoxy. Not even if JSR asks you nicely.

If cost is an issue, I'm sure an epoxy endcap will be just as effective as a PVC one and no doubt a damn sight cheaper.

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Haha JSR my bad
Alrighty so shock pump is off the list.. thats kind of good actually..

JSR:
I was planning on using the blow forward design that uses an alloy bolt slider..the design that stemmed from the seringe design, I cant find the friggin link now sorry I had also considered that other valveless design, but I would be a little worried about its capability of easily firing single shots.. I dont want to be spraying like crazy, and with a small tank I wont have the capacity either.. what do you think?

id sagest using a blow gun as you main valve and getting a cap gun to hit the valve stem as hammer.

Not 100% sure what you mean by this? I was just planning on using a blow gun as the valve, running straight to breech/barrel/whatever design I go with.. And when you say weak, how weak are we talking?
I mean, the thing doesnt need to be crazy powerful, if all turns out well and cheapish I'll be making about 5 so our house can have a little warfare.. proper safety of course
but then again, I would like it to pack a little punch, at least enough to really not want to get shot by it..


thanks for the quick replies by the way.. JSR your knowledge and intuitive nature astounds me.. hats off to you mate.

what state you in if you dont mind me asking

I'm in Brissy.. There many Aussies on here? I would think there would be a few due to our incredibly tightness when it comes to airsoft/paintball etc

[jackssmirkingrevenge]

I was planning on using the blow forward design that uses an alloy bolt slider..the design that stemmed from the seringe design, I cant find the friggin link now sorry I had also considered that other valveless design, but I would be a little worried about its capability of easily firing single shots.. I dont want to be spraying like crazy, and with a small tank I wont have the capacity either.. what do you think?

You mean this one? I think it would waste too much air for the portable setup you have planned, because a large portion of gas energy is going into cycling the bolt.

If you want to fire single shots, why not make the valveless/popoff design with a straight pull manually reloading bolt?

You could conceivably configure it with an airtight magazine placed in such a manner that if you lock the bolt back, it will give you automatic fire.

Here's what I mean for single shots:

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I was more so thinking this one

http://www.spudfiles.com/forums/viewtop ... tml#113830

Is it any more efficient?
What I dont understand is, what is the difference between me running mine at 150psi from a chamber and you running yours at 150psi from a compressor? Besides of course I will have to pump it, how will it loose any power compared to a gun with the same setup running off a compressor like you did in your first testing of that design?

hmmm I see what you mean with the cocking bolt.. and I dont mean to shut it down, but that sort of gets rid of the whole semi idea I really wanted to achieve.. In the original valveless popoff link you sent, he said that he had a good trigger range and was able to fire off single shots.. that tank is about the size I plan on running.. It seemed to have quite decent power at 200psi.

Though I really like the breech with moving bolt.. seems so much cooler
ahhhh so many ideas and options.. This is killing me

[jackssmirkingrevenge]

I was more so thinking this one

Is it any more efficient?

Given the much smaller dead volume, no doubt.

What I dont understand is, what is the difference between me running mine at 150psi from a chamber and you running yours at 150psi from a compressor? Besides of course I will have to pump it, how will it loose any power compared to a gun with the same setup running off a compressor like you did in your first testing of that design?

When you have a 25 litre compressor, you won't really notice wasted air. When you have a 0.4 litre air chamber you have to pump manually, you'll appreciate the difference.

Though I really like the breech with moving bolt.. seems so much cooler

I know exactly what you mean, and the amount of blood, sweat and tears I have put into reciprocating bolt systems and ejecting cartridges over the years is a clear illustration of that, but if you're limited to a hand pumped chamber, I would compromise and go for something similar to lozz08's project.

ahhhh so many ideas and options.. This is killing me

Welcome to spudfiles

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Alrighty well thanks alot for the guidance.. Wednesday is going to be a big day for me, released from hospital and straight into building..
will go with lozz08's design first and see how I go with single shots..

will whip up a progress thread when i get there..
thanks again

[jackssmirkingrevenge]

Good luck

And when you say weak, how weak are we talking?
I mean, the thing doesnt need to be crazy powerful, if all turns out well and cheapish I'll be making about 5 so our house can have a little warfare.. proper safety of course
but then again, I would like it to pack a little punch, at least enough to really not want to get shot by it...

Here's an idea of what the humble blowgun can achieve with a decent sized barrel and shop compressor pressures.

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Well Im sure that will provide a bit of a sting if it were to get you on some bare flesh

thats awesome..
oh oh, one more question.. I see lozz08 has a short clip with a silicone sort of pressure fit..
I was thinking more along the lines of a gravity fed hopper which can hold a whole lot more bb's.. does there need to be any restriction as the bb's leave the mag and enter the barrel? Or will just a straight unrestricted hole into the barrel suffice? Obviously the mag will need to be airtight also considering there will be no breech setup yeah?

[jackssmirkingrevenge]

Well Im sure that will provide a bit of a sting if it were to get you on some bare flesh

I'm assuming though you wouldn't use lead pellets... incidentally, can you get airsoft BBs? Most Aussie members seem to have difficulty obtaining them.

I was thinking more along the lines of a gravity fed hopper which can hold a whole lot more bb's

Just flip the tee around, but remember, the whole hopper has to reach popping pressure before it fires, so the bigger the hopper the more air you will use per shot.

will just a straight unrestricted hole into the barrel suffice?

Yep

Obviously the mag will need to be airtight also considering there will be no breech setup yeah?

Yep

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I'm assuming though you wouldn't use lead pellets... incidentally, can you get airsoft BBs? Most Aussie members seem to have difficulty obtaining them.

Well I read in another thread that if you ask them to label it as "slingshot ammo" it can get through customs... some loophole or something, where they are legal as long as they are only used in slingshots... I ordered 4000 6mm BB's off ebay yesterday, coming from the uk.. so we will find out wont we

[inonickname]

I'm assuming though you wouldn't use lead pellets... incidentally, can you get airsoft BBs? Most Aussie members seem to have difficulty obtaining them.

Well I read in another thread that if you ask them to label it as "slingshot ammo" it can get through customs... some loophole or something, where they are legal as long as they are only used in slingshots... I ordered 4000 6mm BB's off ebay yesterday, coming from the uk.. so we will find out wont we

You'd better hope the seller marked them. When I ordered some he didn't mark them as slingshot ammo (yeah, great, nothing against asians but if you're going to sell something on ebay you should know how to speak english) and customs confiscated them. I got a nice letter telling me next time i imported something illegal i'd be prosecuted.