My dad still has not ordered the lathe and mill yet so I can't get started on my PCP yet but I am very eager to build and shoot an air rifle because I am so bored waiting.
I want to build a coaxial air rifle that is made from aluminum. This gun will be made for pure accuracy and hopefully be able to shoot 2 inch groups at 125 meters max. The gun will be pressurized to 100 psi - 150 psi. Any higher pressure than this will be too loud. (And of course I'll build a silencer for it.)
I also want this gun to look nice and I'll make a nice stock for it as well. So for a pilot I would like to use a schrader valve. I'm thinking of using a 1/2" aluminum pipe for the outer body and a 8mm aluminum pipe for the barrel. The whole gun is planed to be 70cm long total but the pressure chamber will be cut off half way down the barrel because the gun is so long that the air right at the end of the gun will never reach the projectile in time to benefit it and it will slow down recharging. So my first question is, will the schrader valve be big enough to pilot the gun?
Secondly, because this gun will be used at 150 psi maximum, I want to use an aluminum dowel that will fit snugly inside the 1/2" pipe and use that as end plugs which I will epoxy in. So my second question is: Will epoxy safely hold 150psi?
I was thinking of ways to reduce sound as much as I can. So I thought of using a spring with some rubber on the end of it behind the piston to act as a bumper and absorb impact sound and prevent damage to the gun.
I will design a projectile that will be accurate and create it on the lathe, for now I will use darts because I don't have the lathe yet.
Please don't be mistaken, I will be building that PCP I have been designing but I can't because I haven't got my machinery yet, for now I'm building this for recreational purposes.
both of them use 400psi and they wouldnt even be capably of that accuracy, 150psi just isnt going to cut it, also if you have a tight enough piston you may be able to use a schrader valve but you will probably wont something a little bigger, i use one on my cane gun though and it works fine
I remember seeing an air gun called "copperhead prime". That gun used that same valve in the link above and shot potato at 300 meters. Can't remember the psi and I doubt it shot accurately but this project is worth the shot. Aim: to build an air rifle that will shoot very accurate at long distance.
Re: 1/2" Aluminium Coax
Posted: Thu Jan 26, 2012 2:58 am
by jackssmirkingrevenge
DerpWithAGun wrote:I want to build a coaxial air rifle that is made from aluminum. This gun will be made for pure accuracy and hopefully be able to shoot 2 inch groups at 125 meters max.
Very optimistic, I can barely manage that with this.
The gun will be pressurized to 100 psi - 150 psi. Any higher pressure than this will be too loud. (And of course I'll build a silencer for it.)
With a fast valve and large chamber, even at that pressure it will be pretty loud.
So my first question is, will the schrader valve be big enough to pilot the gun?
If the piston is tight enough, yes.
So my second question is: Will epoxy safely hold 150psi?
I've used this construction method in 800 psi pneumatics and 3000 psi hybrids, mostly with no problems. mostly
I was thinking of ways to reduce sound as much as I can. So I thought of using a spring with some rubber on the end of it behind the piston to act as a bumper and absorb impact sound and prevent damage to the gun.
The noise of the piston impact is negligible compared to the muzzle blast.
I would make the chamber the full length of the barrel, if you're running at sub 150 psi you'll need the extra air.
I remember seeing an air gun called "copperhead prime". That gun used that same valve in the link above and shot potato at 300 meters.
You'll be hard pressed to hit a barn door with a potato at 50 metres, I somehow don't think you're recalling correctly... of course one might reach the distance, but actually hitting a point target is something else entirely.
Posted: Thu Jan 26, 2012 8:37 am
by DerpWithAGun
I will be creating something similar to this metro gun definitely. It wont be a coaxial but I have a great idea! (already drew up some plans) See where the pump handle is? That cylinder looking thing will be the air chamber. Directly above that will be the piston assembly. Then there will be a few more parts that will lead up to where the trigger is. That trigger will be a blow gun and it will be the pilot. The pressure chamber at the back of the gun will be another air chamber. I will fill up that chamber via schrader valve and I will use it as a filling chamber. I'll open that ball valve directly in front of it and that will fill the gun, then I'll close it again. This will allow for 2 or 3 shots per recharge. I prefer 1 shot anyway for more power.
The reason I chose the double air chamber is because It looks awesome. Could someone please tell me if my idea of two chambers will work or be powerful? Or maybe I should use that second chamber at the back of the gun for good looks and don't connect it to anything, though, that would be kind of useless.
The piston I'm going to use will be made from a PVC pipe filled with either epoxy or hot glue. I'll put some rubber on the end of it. The PVC pipe I have fits very snugly inside a 3/4" connecter!
I think I may be dreaming a little bit about making this shoot 2" groupings at 100 meters or so. Maybe 50 meters max?
Anyway, off to the hardware store tomorrow, I'm only going to buy parts for the piston and piston housing only, in case it doesn't work so I don't waste any money.
Okay just did some research on QEV valves. I found this one from wyzz:
Wyzz's one looks great and I think I have all the parts for it, want me to upload a picture of all my parts and then you guys can give me some ideas? I don't fully understand how a QEV works but I think it's similar to a piston valve except it has multiple shots??
As for slide valve, probably not. I enjoy loading the bullets in myself. Although semi-auto would be sooooooooo damn fun! Maybe I can make that on the lathe instead of the PCP.
Anyway, I'm gonna do the best I can now and follow Wyzz's tutorial!
(I hope its multishot)
DerpWithAGun wrote:Okay just did some research on QEV valves. I found this one from wyzz:
Wyzz's one looks great and I think I have all the parts for it, want me to upload a picture of all my parts and then you guys can give me some ideas? I don't fully understand how a QEV works but I think it's similar to a piston valve except it has multiple shots??
A QEV is a piston valve you can purchase from a shop, they are functionally identical.
To get multiple shots from one tank depends on how you configure it.
Posted: Fri Jan 27, 2012 3:26 am
by Petitlu
yes jack but the "home made" a lot of charm!
plus you can put a lot of pressure in the QEV HM, mine runs at 870psi
Posted: Fri Jan 27, 2012 3:31 am
by jackssmirkingrevenge
Petitlu wrote:yes jack but the "home made" a lot of charm!
Bien sur, can't argue with that - but sometimes it's easier to just buy something, especially for those with undeveloped technical skills and understanding.
plus you can put a lot of pressure in the QEV HM, mine runs at 870psi
HPA for the win
Posted: Fri Jan 27, 2012 3:35 am
by Petitlu
Posted: Fri Jan 27, 2012 6:29 am
by DerpWithAGun
Alright, so if I make a shorter piston and add a spring behind it, when the pilot valve is opened the piston will shoot backwards momentarily and then close again? Allowing for multiple shots??
Quickly tell me now if this is true as I'm going back to the hardware store tomorrow to buy more parts because I stuffed up on the sealing face of mine. (PVC connecter, hammered in a piece of PVC pipe and then epoxied an aluminum pipe into the PVC one, the Aluminum pipe was cut too short.)
JSR, would it be possible to remove the pipe? It was a VERY tight fit in the pipe anyway and I added epoxy to seal it up.
I might just make a gun that looks like this: 
