Spring Airsoft Gun; Take away spring?

Building or modifying BB, Airsoft, and Pellet type of guns. Show off your custom designs, find tips and other discussion. Target practice only!
WizardNoodle
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Thu Apr 13, 2017 4:47 pm

So after I acquired my cousin's old & broken Airsoft spring rifle, I actually became more intrigued in the sport. I have never played and probably will never play an official game but it sounds like a fun thing to do with friends.

Anyway, I was looking at all these spring guns, as they are both the cheapest and simplest and I want to have a full understanding of how it works and to be able to learn how to take them apart and modify them, and my question is if you sealed the area where the main spring lies, and added an O ring pair to the piston connected to the spring, could you inject some pressure and replace the spring with air? It seems like it wouldn't wear down like a spring, and you could easily adjust the power by pressure. Here is how I understand it would work:

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Is this something that could work, or if not why or is there something I can change even further?
Also, maybe I could experiment which gasses are better- my guess is the harder to compress the better it performs?
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jimmy101
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Fri Apr 14, 2017 9:59 pm

Yes, that will work. But you'll loose a fair amount of the energy you put into the system when you compress the gas. Compressing the gas heats it up. Gas gets pretty hot but has low heat capacity compared to the cylinder walls so that energy transfers to the walls of the cylinder and is lost to the rest of the universe. When you fire the gun the gas expands and cools off. The cooling reduces the effective pressure in the cylinder and the piston doesn't return to its starting position during the firing cycle. As the gas warms up via heat transfer from the cylinder the piston will move back to its original starting position but that happens after the ammo has left.

Overall it would work fine if done carefully (not too much friction in the o-ring), you loose some energy because of the compression heating but compared to other methods of generating force it wouldn't be all that bad. (Guns are more like 5% or less efficient. Gasoline engines are roughly 30% efficient, combustion spud guns are a couple percent efficient, compressed air guns probably less than 20% efficient.)
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WizardNoodle
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Sat Apr 15, 2017 10:25 am

jimmy101 wrote:Yes, that will work. But you'll loose a fair amount of the energy you put into the system when you compress the gas. Compressing the gas heats it up. Gas gets pretty hot but has low heat capacity compared to the cylinder walls so that energy transfers to the walls of the cylinder and is lost to the rest of the universe. When you fire the gun the gas expands and cools off. The cooling reduces the effective pressure in the cylinder and the piston doesn't return to its starting position during the firing cycle. As the gas warms up via heat transfer from the cylinder the piston will move back to its original starting position but that happens after the ammo has left.

Overall it would work fine if done carefully (not too much friction in the o-ring), you loose some energy because of the compression heating but compared to other methods of generating force it wouldn't be all that bad. (Guns are more like 5% or less efficient. Gasoline engines are roughly 30% efficient, combustion spud guns are a couple percent efficient, compressed air guns probably less than 20% efficient.)
If I installed a piece of PVC pipe, and the piston moved inside it, with the O-rings being greased, it should be pretty thermally insulated, minimizing energy loss, right?
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jackssmirkingrevenge
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Mon Apr 17, 2017 8:52 pm

Anyway, I was looking at all these spring guns, as they are both the cheapest and simplest
While simple in concept, they require very strong construction if you want reasonable power, not a route I would recommend for home building.
could you inject some pressure and replace the spring with air?
Look up gas-ram rifles.

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How spring airguns work: http://www.arld1.com/pistonpelletdynamics.html
hectmarr wrote:You have to make many weapons, because this field is long and short life
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