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ok so i was just laying around thinking and i think i figured out how to make a semi-auto combustion.
to really understand this it would probably be best if you understood how an autococker paintball gun works but instead of a hammer sliding forward, an explosion goes off in the chamber
now for the gun design:
so it starts as a stacked tube design, with your barrel mounted over your chamber. I was thinking a 2.5" tennis ball barrel over a 3" combustion chamber.
in the lower tube a fan is placed in the end that will be the "front" and then that end is sealed off with whatever kind of cap you want but a threaded endcap would probably be best for this situation as it lends itself to expansion later on if needed.
both tubes are then mounted in parrellel (sp?) so the "rear" end of both are flush but DO NOT permanently mount the two in place just yet
now you need to start work on the backblock. for the bottom part of the backblock you need a rubber stopper that will completely plug the bottom tube and allow no gases to leak. for the top part you will need a bolt that is just like 99% of all paintball gun bolts so that the air can be diverted in a 90* bend. the bolt needs to slide in and out of the top bore smoothly so that it won't funk up the rythym.
next you need to take your two tubes and drill holes in them that match up with the hole that is on the side of the bolt so the expanding gases can flow from the bottom tube up through the hole and through the bolt to propel your ammo out the barrel.
after all of that matches up you can then permanently mount the barrel and chamber together.
next your going to need some electro-magnetic solenoids that have enough throw to move your bolt back enough to let your ammo drop smoothly into the bore. (in my design since a tennis ball is roughly 2.5" in diameter I will need something with at least a 2.8" throw if not upward of 3"). using at least two (one on each side of the gun but possibly more) mount them so that they will push the backblock back to vent the chamber and load another round.
now pull your backblock back to its rearmost position and drill a hole in the top for your ammo to drop through
after all that is mounted you should have a nearly finished gun. in my idea it needs a control board that controls the timing between firing and the time that the backblock opens and i was thinking possibly a copy of a paintball gun board to do this.
ok so this pic is after the ball has been fired.
the backblock moves back opening the breech to allow another round to drop in and it opens the combustion chamber for the unused and leftover gasses to be vented.
the red is the air passage between the two pipes for the gasses to go through the bolt when it is in the closed position. the blue is the chamber fan. and the black is whatever is used to move the backblock
and here is a cutaway of the bolt
I also have alot of minor and asthetic upgrades i would like to do if i ever get a chance to build this.
lmk what you guys think about this idea
i think you have to much text, when people see this they don't care to read it all and go back to another thread.
shorten it down a bit
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I just skimmed your post so I may have missed it, but what keeps the combustion gases from blowing out that plug/bolt assembly when you fire the gun? You're looking at around 700 lbs of force pushing on the 3" chamber plug and 500 for the barrel.
If your looking for a circuit controlled semi-auto combustion without a terrible concern for ROF then it wouldn't be too hard to do with a mattress inflator/check valve setup for exhaust, an electric actuator on a standard bolt for loading, and an electric 3-way valve for fueling.
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clide's right, its also the first thought that comes up with me.
That plug WILL embed itself into your belly unless you secure it REALLY GOOD.
If you are not 100% sure of it, it is a dangerous thing.
Its zero-tolerance, one part fails, and the operator of the gun gets a kick in the tummy he will never forget.
Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!
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why not build a tippmann 3C type of gun but then with a 3 way valve so that it could function just like an autococker?
But yeah... I dont think it is doable anyways to make a homemade combustion auto gun bc of increasin heat problems.
have you ever felt the pump stroke on a c3? it is a very stiff stroke, far to heavy for lp pneumatics to control.
heat would be a solvable problem but overall I think my idea is best
Seems like a complicated way to vent the exhaust(?)
What about a semi-auto/auto design, using pressurized air/oxygen and fuel.
The fuel enters the chamber. Pushes a (small) blow-forward bolt completely forward (Loading). Closing a contact (switch) located in the bolt. If the trigger switch (series with bolt switch) is closed, the ignition spark fires.
Perhaps a simple two part trigger. To mechanically press or open a valve (venting exhaust). Then pushing further back to close the electric switch triggering the ignition.
I prefer another method of venting the exhaust mechanically. But my brains are feeling scrambled trying to design an automatic mechanical vent somewhere (that will close before fueling).
It would be nice to keep the electronics a few switches and the ignition.
Last edited by THUNDERLORD on Thu Sep 11, 2008 3:33 pm, edited 1 time in total.
I don't think that heat will be a problem... as long as you use metal you should be fine.... normal guns work ok with much more heat per shot
whether a semiauto combustion is practical or not is a different story... you know there are hardly any semiauto pneumatic guns.... and I suppose that they are several times easier to build than combustions....
but if you want to build it go for it...
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Semi-automatic pneumatic guns are pretty damn easy to build, they just require a little tweaking and African Ingenuity to get right.
Also, as to those who think this post has a serious case of the TL;DR's, it's actually a pretty short post. Sit your lazy ass down and read it or don't comment.
As to the design:
1.) How will the air flow effectively out the back of the launcher with the front of the chamber capped off? You'd get little to no flow without that end of the launcher open to the atmosphere to allow good airflow. I'd probably suggest adding a stronger fan and adding a "chamber check" to allow good flow.
2.) Instead of a paintball board, you could probably utilize a 555/556 IC to do the timing aspect for you.
When I was thinking about building a 6mm semi auto for airsoft, I thought hard about using a combustion. My hypothetical venting design involved the blow forward bold sealing the hot gas after combustion. as the gas cooled, it would begin to pull a vacuum in the chamber, which would pull fresh air into the chamber from the atmosphere. This has never been tested, so feel free to slam my idea, I have no proof. I agree with the use of a 555/556 timer. My main reason for not building it was the heat melting o rings and the valve seats melting. just my $0.02
I didn't mean specifically a paintball board. just something similar.
iim still working out some kinks before I prototype it
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