Introduction: Repeating Airgun Ball Valve Triggering (DIY)

the operation can be found in this video

http://youtu.be/IJpMpPN5Gnw

P/S: my first instructable, sorry for the video embed failure. I dont understand how to do it

http://www.youtube.com/watch?v=IJpMpPN5Gnw

initial sketch done with google chrome (cool program, try it its fun). initially drew the pipe fittings and saved each as a component. then sketchup remembers each pipe fitting and i just need to copy, paste, and arrange the pipe fittings.

Most times, people just make their airguns as single shot. Sure, its more powerful, but unless you have a d*mn good barrel to go with the gun, most of the air is going to be wasted. Plus, how are you gonna do a double tap with a single shot airgun or what if you miss? (assuming you cant own firearms)


The basic principle of this gun: Instead of just a reservoir to keep the pressure, I made 2. one as the reservoir and one as a chamber to shoot the bullet. So thats why I use 2 ball valves. I ball valve between reservoir and chamber one ball valve between barrel and chamber. First, you close the trigger and pump it. Then you close the reloading valve. then you shoot by turning the trigger valve. close the trigger valve back. and you open up the reload valve (and close) to renew the pressure in the chamber

Operation: after shooting with trigger valve. you open another valve so that the air pressure in reservoir can fill into the chamber. so you can shoot again.

Step 1: Triggering

CHAMBER: you need to be sure that it is not too small, or not the shot would be too weak. I use about 1 meter length of pipe in total (in the shape of a square). It must also not be too big, or not it will drain too much pressure from the reservoir when you reload the air. when the chamber has too little pressure until the bullet starts curving downwards too much, dont be stingy and just use up all the pressure in the gun. Open the reloading ball valve and shoot your last shot. No use shooting several weak shots that wouldnt even deform a can. Will use up all the pressure in the reservoir and the chamber

RESERVOIR: The pressure drop should be exponential If im not mistaken. The shot keeps getting weaker as you shoot. And how many percent it drops should depend on the size of reservoir and chamber. Always stick to 1.5 liter soda bottles if you intend more than 2 shots. Which means that the pressure will drop by a percentage of the previous shot. E.g. you charge gun to 100 psi. first shot is at 100, then if the second shot at 90 (10% lost) so the third shot should be  81. then 73 psi then 66 psi then 60 psi.... etc etc

you can either use PET or steel. Im not that advanced to do metalwork, so i guess ill just keep with PET. So thats why I cant go beyond 100 psi or it would burst

I made the reservoir replaceable because if I merely glue it on, and the pressurised bottle bursts, the gun would be useless. I just used some tighteners with 3 zip ties to hold the bottle. Also, giving one or 2 layers of cellophane on the pipe end helps seal the pressure, if you want to use some weak glue as sealant, thats your choice. But I sometimes bring my gun into water and some always gets into the reservoir, so I eventually need to remove the bottle after every use. This type of gun is quite reliable because many parts can be repaired if damaged. unless if a huge section of the pipe gets broken, then its just junk or just some memorabilia of an old project

directions on the connection between reservoir and the gun. i did without melting the pvc for a bulge. i merely add a layer of cellophane to seal the small gap between bottle and pipe. find this link below:

www.youtube.com/watch?v=icQhLT4QCO8

Step 2: Pressurising the Gun

BICYCLE VALVE: I want the gun to be repairable in case of damage. So instead of drilling a pipe endcap and inserting in inside, I glued a bottle neck to the pipe. Then I drilled the bottle cap and glued the bicycle valve to the bottle cap. In case of damage, I can unscrew it and see whats inside

The PVC glue I used does not melt PET bottles. test some of your glue in a small piece when in doubt. Its not really glue, its PVC solvent, so if It cant melt PET, it wouldnt hold. Use some strong glue and use a knife to scratch the PVC pipe and inside the bottle neck before gluing

P/S: the middle tee that has the bottle cap needs a little modifications. slightly angle the tee maybe 10 degrees, so that the pump can be attached more easily. I put it there so that it will be hard to damage i.e. dropping or by getting hit. but remember that angle it outwards not inwards because there will be the air reservoir if you angle it inwards, could mess the whole project when the glue hardens

Step 3: Additional Modifications

BARREL: at first i didnt really have a reload mechanism, I just remove barrel to put in another bullet. Now I use a larger pipe (20mm pipe) to slide back and forth so that I can reload at the breech. That is if i use my papier mache bullets or marbles. Darts, I still need to remove the barrel to reload the darts.

Long barrels are powerful because thy maximize the energy. When the bullet goes out at the end, the leftover pressure are discarded. I use about 2 feet. I even tried 4 feet and theres still energy wasted. But I scrapped the idea because 4 feet barrel is too long and hard to hold. But It became too powerful to be called a toy. So im sticking to 2 feet.

AND remember not to glue the barrel to the ball valve because you probably could try invent a bolt action for the bullets, easier reload. Or you could attach scopes or other gadgets. Plus, you can make the gun compact because it will take less space when you keep it

P/S: i was using papier mache bullets. please pardon the awful looking ammo. but it fun, you can get shot by it and not feel more than a sting. i have nail darts and marble bullets but for a toy, newspaper papier mache it is

SCOPE: The gun wobbles a little as we turn the ball valve and accuracy is greatly reduced. You can try using QEV if you want to. The accuracy shouldnt be that high, so its ok if you want to make only front sights like a shotgun. But I made front and rear because I play with my gun often and I know how much force to use so that the gun is balanced and doesnt wobble much.

1) get 2 PET bottles with their neck able to fit just little tight around the barrel. cut off the main body to obtain just the bottle necks.
2) Make 1 notch on the rim of each bottle neck. not too wide, just around 1 mm notch
3) insert the bottle neck to the barrel, you can choose how far you want the read and front ends to be
4) If they are too loose, you can add maybe one layer of cellophane tape
5) find a suitable object to hold the barrel so it doesnt move
6) now "calibrate" the sights by looking inside the barrel, find a "reference point". e.g. a switch, a number on your clock, a tiny    object quite some distance away. then adjust the sights to be aligned with the "reference point".
7) repeat 6) a few times. I once got a nail dart to hit exactly where I wanted it to from about 30 feet (~10 meters). Then I never messed with the alignment anymore. Yes it could be a lucky shot but i was contented with it already

if you look closely you can see one notch at the green mountain dew bottle neck and another notch at the regular bottle neck which has red markers for visibility 

FLASHLIGHT: Not really as good as expected but I guess the picture explains it all. Im not very optimistic about laser sights for small DIY projects. Because most laser pointers dont really point straight through its axis, and you dont use the best material for DIYs, that way, you cant calibrate the laser and forget about them because after a while(ie using tapes to secure laser to gun), they shift and you will shoot and miss. want laser real bad? invent something rigid that will definitely hold the laser without shifting

Step 4: Some of the Tools/components You Need

ALL parts are 15mm pipes unless stated as not

2x ball valve
4x 90 degree elbow
3x tee
1x 500ml bottle (for the bicycle valve)
1x 1.5 litre bottle
1x bicycle valve
3x zip tie

1x flashlight. best if you have a strobing one. cool stuff so you dont necessarily need to fire at someone. Also in the middle of the night it is a subtle way to say F**k off my garage, I have a gun, and you cant see it properly because of the strobing effect, so you better back off before i change my mind and just shoot you. (p/s in self defense try aim center mass or pelvis, easier than flailing arms or feet)

not really 1 roll, thats just the minimum u need to buy if you dont have one. but who doesnt eh? I even keep tapes in my get home bag, whenever i go out. Just in case. shit happens ya know. So always be prepared
1x roll of duct tape. for the gap between the 20mm pipe and the barrel
1x roll of cellophane

2 feet pipe for barrel (the one in the picture is the previous version, too short for practical use)
2 inch 20mm pipe
around 4 feet for joining the components. there may be some extra pipes
1x PVC pipe glue
When gluing the parts together, plan what to glue first and what to join first. how are you gonna join 2 perpendicular pipe with a 90 degree elbow? so plan well.

A suitable hollow cylindrical piece of plastic as the "clip" to hold the zip-ties to hold the bottle
2x rubber hose tightener. seriously, 1 isnt enough. and I was using just 50 psi

tools?
I only used a knife and a hacksaw blade without the handle. yeah, it sux to have to use newspaper to hold the blade. thats what I found at my house. I almost cut my finger once (just a scratch, probably some capillary bleeding, was nothing).

Actually I didnt drill the bottle cap. I dont have a drill.... I just use multiple hard objects to punch a hole through it.

and also you could either cut off the extra zip tie or tuck it in the hose tightener. see how messy it looks in the picture here. It looks like some ninja grappling hook, but it feels like a cockroach antenna. Fine if you like it that way, but this is just a suggestion. This photo is old and I keep them tidy now.

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Bio: Im just a student. Doing A levels to try learn Mechanical Engineering in the UK.
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