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Piston not sealing..

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Piston not sealing..

Unread postAuthor: spudthug » Wed May 16, 2007 3:18 pm

ok guys i am making a btb replica sawed off shotgun..it will be done as soon as i get my piston done.. what i need toknow is how u guys usually put a threaded fitting throguh another threaded fitting so it goes halfway into the tee? is there different methods of this? i need help or i am going to have to make it out of copper...and i really dont want to... t


thanks- Mr. Potato Pimp
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Last edited by spudthug on Sat May 19, 2007 11:36 am, edited 1 time in total.
4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: schmanman » Wed May 16, 2007 8:07 pm

oh boy, another btb shotgun replica! there's only 200 of those out there! :wink:

when I built my bb rifle, I did it differently.

I was (sorry if this sounds like bragging) the first to thread it in from the opposite side of the bushing, then there were other valves built like that. I just found a nipple that got narrow enough at the end to screw in from ther opposite, teflon taped it, then screwed it a little over halfway into the valve. I then stretched a piece of surgical tubing over the pipe, as the sealing face (I like to make the sealing face on the inside of the valve, not the piston).

yeah. well, do it however you want, but this way is relatively easy, unless you have to tap the fitting from the opposite side. or grind down the pipe nipple to fit.
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Unread postAuthor: Velocity » Wed May 16, 2007 8:16 pm

schmanman wrote:oh boy, another btb shotgun replica! there's only 200 of those out there! :wink:

when I built my bb rifle, I did it differently.

I was (sorry if this sounds like bragging) the first to thread it in from the opposite side of the bushing, then there were other valves built like that.


Is that <a href="http://www.spudfiles.com/forums/metal-piston-valved-cannon-t3953.html">so</a>?
haha you actually beat me to it by 6 days I think? Though I really liked your BB rifle, I'm not sure it inspired me to make the barrel port that way; I think I was just running out of time and did it as a last ditch effort

Anyways, I did not really like the reverse nipple screwing in way, just because I felt that it was prone to leaks. I just filled the whole metal bushing with epoxy to insure that I didn't get any leaks on mine. IF I were you, I would just buy a copper male adapter, a copper bushing, and a piece of copper pipe to use as the barrel. You can pass the copper barrel into the tee by drilling out the bushing and soldering it to the copper male adapter. :lol:
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Unread postAuthor: spudthug » Wed May 16, 2007 8:44 pm

oh boy, another btb shotgun replica! there's only 200 of those out there!


Really?? i have only seen one..jims, or known as lucy in the sky on here... but whatever.. oh and tthat wasnt even a replica it used a QEV and he said it wasnt powerful and it wasnt used at high pressures.. but oh well

i have fixed the psito nin the tee problem because i was bored waitng for people to reply so i tried to stick a copper pipe throguh a 1"x 3/4 bushing...my luck it went through i expected it not to hehe.. but anyway i jb welded it there and now it it halfway throgu hthe tee..

so then i went to buteras ( local hardware store) and bought a 1" x 3" nipple.. i found that it had a line where the seam was where the pushed it together or whatever.. now i have to grind it out with a frigging lathe...
more time.. oh well i had to use the lathe anyway for my piston.. i cant wait till this is done..


ok a biit off topic but u know those c02 refill things that are used for bike tires?? the 12 gram ones?? i need to know some things...

1. do they have a max pressure on them or can they go to like 300 psi without stopping? or do they have like a stop at 100 psi or something... if so how can i break that stop and fix it so it wont leak?

2. how much psi do u think 1 12 gram will put into a 1.5" x 10" chamber??
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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: CS » Wed May 16, 2007 8:50 pm

*titty bumping stops here*
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Unread postAuthor: Velocity » Wed May 16, 2007 8:54 pm

Well first calculate the volume of your chamber
((1.5/2)^2)(pi)(10)

its about 17.67 cubic inches

Next, consult the 12 Gram CO2 chart in the spudwiki.

For a 20 cubic inch vessel, a 12 Gram CO2 cylinder will fill it to 210 PSI... so you will probably get about 238 PSI in that chamber

Be careful...
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Unread postAuthor: spudthug » Wed May 16, 2007 9:04 pm

Well first calculate the volume of your chamber
((1.5/2)^2)(pi)(10)

its about 17.67 cubic inches

Next, consult the 12 Gram CO2 chart in the spudwiki.

For a 20 cubic inch vessel, a 12 Gram CO2 cylinder will fill it to 210 PSI... so you will probably get about 238 PSI in that chamber

Be careful...


yay!! i was hoping for atleast 250 psi but this will do. thanks for ur help rmich and do u know if the fillers have restrictions??
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Unread postAuthor: schmanman » Fri May 18, 2007 8:02 pm

spudthug wrote:
oh boy, another btb shotgun replica! there's only 200 of those out there!


Really?? i have only seen one..jims, or known as lucy in the sky on here... but whatever.. oh and tthat wasnt even a replica it used a QEV and he said it wasnt powerful and it wasnt used at high pressures.. but oh well

i have fixed the psito nin the tee problem because i was bored waitng for people to reply so i tried to stick a copper pipe throguh a 1"x 3/4 bushing...my luck it went through i expected it not to hehe.. but anyway i jb welded it there and now it it halfway throgu hthe tee..

so then i went to buteras ( local hardware store) and bought a 1" x 3" nipple.. i found that it had a line where the seam was where the pushed it together or whatever.. now i have to grind it out with a frigging lathe...
more time.. oh well i had to use the lathe anyway for my piston.. i cant wait till this is done..


ok a biit off topic but u know those c02 refill things that are used for bike tires?? the 12 gram ones?? i need to know some things...

1. do they have a max pressure on them or can they go to like 300 psi without stopping? or do they have like a stop at 100 psi or something... if so how can i break that stop and fix it so it wont leak?

2. how much psi do u think 1 12 gram will put into a 1.5" x 10" chamber??


well, there's killa's, there's several ball valve ones, demon's, and some more.

hope it works out for ya!

rmich, I remember that gun. I have never once had a leak there. I used some tfe paste, which contains teflon, and also makes a great piston lube, since it's thick.

is that gun still together?
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Unread postAuthor: Velocity » Fri May 18, 2007 8:08 pm

schmanman wrote:
rmich, I remember that gun. I have never once had a leak there. I used some tfe paste, which contains teflon, and also makes a great piston lube, since it's thick.

is that gun still together?


Yeah, my gun never leaked either... I just thought that it would :lol: .

That gun is not still together; it only lasted about a week or so. I was shooting it in the cold weather, and the piston cracked, because it was made of PVC. Instead of replacing it, I just left it be. It was never an incredible gun; I never actually saw its full potential though.

Even though that particular gun has lasted the shortest amount of time compared to my other guns, as well as it was fired the fewest, I still receive a lot of PM's asking me about it :lol:

Honestly, I could put it back together really quick... build a new piston, clean out the dirt from inside, and reassemble some of the disassembled pieces... but I see no use for that. I already have a winter gun that can take high pressures, and it will out shoot that one any day, even when using half the pressure or less (referring to my most recent copper gun). The only real advantage which that one had was that it was the only compact gun I ever made.... coming in at about 40" long :roll:
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Unread postAuthor: spudthug » Sat May 19, 2007 11:35 am

ok guys a new problem has emerged... my gun is finished piston and all.. but when i jb welded the copper into the iron it dried crooked... so now it doesnt seal right.. but idk why is doesnt seal.. when i took it apart and pulled out the piston it had a mark the whole way around the rubber of where it hit the copper pipe.. so the rubber is touching every where... maybe i have bad rubber...although i used the same exact sheet of rubber for all my other pistons... how can i fix this??
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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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