If you need any small parts made give me a bell . Nothing too big or it will cost a fortune to post half a world away.
It's looking promising so far assuming the action will cycle.
I recently bought a small helicopter so that's draining some of my gun building attention. I'm going to pull it apart tomorrow and custom machine any part I can, then blue all the steel parts (I picked up a bluing kit), then look for or build a new body for it..
Thanks for the offer, as it is I'm trying to keep things simple so the design will be open to those who don't have machining facilities, in the same way that the pen gun was. Indeed so far the design and materials are very similar to the pen gun.
The firing pin spring is going to have to be quite strong to push a new cartridge in place and open the schrader pilot, in this regard I was thinking of making the breech very short with maybe 25% of the cartridge inside, this will shorten the amount of travel necessary.
A friend of mine bought one and we amused ourselves by flying it outside in the sunshine, the light would jam the IR signal and it would just power up at full throttle before cutting out and plummeting to the ground in the end it was in pretty bad shape but some araldite later, voila, the very definition of solid state electronics still going strong...
Back to the subject of this thread, I've tested it at 75 psi and it worked with a satisfactory "pop". I'll give it another 24 hours before trying it out at higher pressures. The next step is to measure the diameter of the pressurised cartridge and make a barrel/breech setup accordingly, in my last cartridge attempt I cast the breech around the unpressurised cartridge then found that the pressurised cartridge wouldnt't fit
By my calculations, with even just 50 psi on the front face of the 3/8" external diameter cartridge there'll be a force of over 8lbs on it, I'm hopeful this means there'll be more than enough energy to eject the cartridge and recock the bolt for the next shot.
Is that 150 or 850?
Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!
Spudfiles steam group, join!
850 or bust
This is what I had in mind for the action, not much different from a conventional blowback system in most submachineguns. According to GGDT there'll be well over 100 psi available when the pellet leaves the cartridge "muzzle" so this should be workable. The force required to open the schrader at 800 psi will be about 5lbs so the bolt spring is going to have to be fairly strong, but 100 psi on the cartridge face will give three times that force so hopefully it will still recock the cartridge. There's also the danger that the schrader might fire prematurely before the cartridge has been pushed in to the breech, some tweaking will definitely be involved.
1) The purple trigger is pulled releasing the spring loaded green bolt
2) The bolt pushes the cartridge forward until it hits the breech face, opening the schrader pilot
3) The cartridge fires, pushing the projectile down the barrel and the cartridge and bolt backwards
4) The base of the cartridge strikes the pink ejector which tips it out sideways while the bolt is caught by the trigger
5) the orange magazine spring pushes another cartridge in place, allowing the cycle to restart.
have you considered hunting for slaves and locking them in your basement.. you know, someone has to assemble that hundreds of cartridges
cool but I am afraid that cartridges might not be practical
Children are the future
unless we stop them now
If I had a basement where I could lock slaves in, they wouldn't be making cartridges
It took me very little time to put this together, seriously it's just a question of cutting the tubes to size, smoothing the edges and roughening the gluing surfaces on my drill-in-a-vice lathe and epoxying them together. The piston is simply punched out a rubber sheet in a matter of seconds, I could happily make say 50 cartridges in a couple of hours.
In terms of power, I doubt it's going to be very impressive, probably only a couple of ft/lbs. I could have gone for much larger diameter cartridges, say 0.75", which would have given more than double the power potential for the same length and a lot more area for the cartridge to be blown back, but in this case it's more out of mechanical interest with a rifle-like cartridge.
It's not practical if you want to make a pneumatic minigun, but for a semi-automatic sawn-off rifle it should suit my purposes and who knows, if it works well I might inspire someone with machining facilities to turn it into a practical proposition
Last edited by jackssmirkingrevenge on Sun Jan 10, 2010 2:34 pm, edited 1 time in total.
Looks good to me, can't wait for the air-powered Bren. One little addition to your piccie above to possibly counter the risk of it going off half-cocked. I take it the pink bit is supposed to push the cartridge forwards to the breech? If you put a weaker spring between the green "firing pin" and the pink bolt face, opefully the cartridge would be chambered fully, and only then would the firing pin depress the schraeder.
Oh and yes RC helicopters sidetracked me too, bought a 6 channel micro-helicopter and learnt how to fly it into things thus needing new spares, and thus eating into money reserves. Still it looked very impressive flying in the snow today.
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More like a cut down BAR, Clyde Barrow style
The pink bit is fixed to the action and is to one side of the bolt, the cartridge base will strike it and be tipped out to the opposite side where the ejection port will be (remember my cartridge fed prototype). As pointed out above, the 5lbs of force needed to open the schrader should stop it from going off prematurely, but if not a two piece bolt could be a solution.
Gets boring eventually
edit: Gave the cartridge a go at 100 psi with a 1 gram pellet, got an amazing 66 feet per second
Last edited by jackssmirkingrevenge on Sun Sep 12, 2010 12:15 am, edited 1 time in total.
Since you are going open-bolt, you will have full auto even if you don't want it. You will need some kind of dis-connector (that's the closed bolt term) type thing to keep from going full auto.
Methinks it would be easier and cooler to go with a closed bolt. Essentially, use a long floating firing pin that goes all the way through the bolt, and is hit by a hammer.
bolt isn't shown, but the pink is a hammer. That would make full auto harder, requiring an auto-sear...
Other than that, nice job, and good luck.
Admittedly a two part trigger would be more reliable, however I think that if the design I presented had a spring loaded trigger, a light pressure would be ok for semi auto while constant pressure would give it potential for full auto.
In the proposed system, it looks as though the trigger has to be reset every single time you fire. Are there any plans on designing the trigger to reset itself so all you have to do is pull the trigger?
"Never tell people how to do things. Tell them what to do and they will surprise you with their ingenuity." George S. Patton
If worst comes to worst why not make a mechanism so a new cartridge cannot be chambered until the trigger is released (and the bolt reset). A two stage trigger would make this work a lot better.
Let's see if it blows back, then worry about the trigger High pressure testing due when I get back from work, then I'll cast the breech on a length of 5.5mm barrel.
JDP12 made an interesting suggestion, drop of ether behind the pellet to boost performance... might "borrow" some ether from the lab and do some testing with the marker gun (similar specifications to the cartridge) to see if it makes a difference.
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