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My breechloading problems

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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My breechloading problems

Unread postAuthor: maverik94 » Sat Apr 11, 2009 4:45 pm

Ok, So I finished building this gun: http://www.spudfiles.com/forums/50-cal-pneumatic-sniper-t17521.html and I decided to make it breech loading. I took some 3/4" pipe, split it held it apart with a dowel, gloed it with some JB weld, put a dowel handle on it, JB welded that, and shot my gun.......It leaked so much air It shot just over half the normal distance.
Here are some pics. How can I fix this?
here are some pics:

looking down the sleeve breech:
Image

top view:
Image

side view, that gray stuff is JB weld, it isnt going anywhere, its pr is 3000 psi
Image


breech mech. on my gun:
Image


Ok, I finnished the breechloading mech, It works great here's the breech closed:

Image

And here it is open:

Image

The o-rings, with some petroleum jelly work GREAT! Thanks for all the help yall!
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Last edited by maverik94 on Tue Apr 14, 2009 8:20 pm, edited 2 times in total.
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Unread postAuthor: Biopyro » Sat Apr 11, 2009 5:51 pm

You need to get something in between the two pipes to create a seal. O-rings would work perfectly, but even duct tape will go some way to improving your problem.
Also try filing the stop out of a coupler instead of using the split pipe unless you need a hole that large.
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Unread postAuthor: c11man » Sat Apr 11, 2009 6:10 pm

i would redue the pipe and use a smaller dowel.
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Unread postAuthor: irisher » Sat Apr 11, 2009 6:14 pm

I have found that a thick application of automotive wax will seal effectively and slide smoothly.
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Unread postAuthor: c11man » Sat Apr 11, 2009 6:25 pm

but that would require repeated applications every once in a while.

anouther option is to drill out the center of a 3/4inch pvc pipe with a 7/8 drill bit. it still leaks but it sounds like it would be better than yours is right now
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Unread postAuthor: irisher » Sat Apr 11, 2009 6:32 pm

Wouldn't that require a drill press.
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Unread postAuthor: maverik94 » Sat Apr 11, 2009 7:15 pm

well, It slides well, but it's a pretty sug fit, But orings would make it hard to slide right?
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Unread postAuthor: c11man » Sat Apr 11, 2009 8:52 pm

orings dont have to make it slide hard but i am not sure how to make it slide easily

technican should be able to help try PMing him
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Unread postAuthor: maverik94 » Sun Apr 12, 2009 8:01 pm

ok, thanks for the help yall. I have figured out a way to fix this, tell me waht you think. Ok, on the barrel (1/2") I will use a brakeline cutter to make a pair of perfectly round slits arount the barrel, on either side of the breech. I will widen the slits a bit with a triangular saw. I will then put an o-ring into each slit. the o-rings will only slightly protrude from tyhe barrel, for a snug, but not really tight fit. The o-rings will also be a little stretched, so they dont have to be glued, and thus can be replaced. I will post pics, and If it works, i may put it in the how-to section. Do you predict it will work? We will see....... Also, I may need to use some kind of lubricant, like vasaline or petrolium jelly to make the cover slide easier, but I may not need that.
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Unread postAuthor: Technician1002 » Sun Apr 12, 2009 8:13 pm

maverik94 wrote:ok, thanks for the help yall. I have figured out a way to fix this, tell me waht you think. Ok, on the barrel (1/2") I will use a brakeline cutter to make a pair of perfectly round slits arount the barrel, on either side of the breech. I will widen the slits a bit with a triangular saw. I will then put an o-ring into each slit. the o-rings will only slightly protrude from tyhe barrel, for a snug, but not really tight fit. The o-rings will also be a little stretched, so they dont have to be glued, and thus can be replaced. I will post pics, and If it works, i may put it in the how-to section. Do you predict it will work? We will see....... Also, I may need to use some kind of lubricant, like vasaline or petrolium jelly to make the cover slide easier, but I may not need that.


Some lubricants make the rubber swell. Check what they are made from and then match to a compatible lubricant. For most of my rings, I pick them up in the plumbing section, so I use plumbers grease for faucets.

If you want easy sliding parts, size the o ring just large enough to fit the inside of the outer part with very little compression then cut the grooves just deep enough to prevent squishing the ring. A little space under the ring is OK. It seals against the edge of the groove when pressure is applied. It is often referred to as floating rings. These seal well and don't bind. I have a youtube video on this under the same username on using o rings in air cannons.
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Unread postAuthor: c11man » Mon Apr 13, 2009 8:04 am

wow i know who to talk to about oring problems in the future...

and i think both ways will work but Technician1002's might slide a little easier
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Unread postAuthor: maverik94 » Tue Apr 14, 2009 8:23 pm

there, It worked. Thanks for the help, it works like a charm!
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