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Spring Piston Rifle

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Spring Piston Rifle

Unread postAuthor: DerpWithAGun » Mon Dec 19, 2011 6:30 pm

I have decided to build a Spring Piston Rifle and that is final. They are simple to make and I know how they work.
It is basically a Piston with some O-rings and a Rubber sealing face that is in a tube with a spring behind it.
I Have searched on this forum for a topic similar to this and I can't find one.

I only need a few questions answered.
Firstly, in commercial spring piston rifles, a pellet is fired at around 700 fps using .22 or .177 caliber pellets. How long is the piston and the piston chamber?

Second, I will probably be shooting .177 caliber pellets or 4mm Steel Ball Bearings. I want to shoot these projectiles at 650 - 700 fps. How long would my spring have to be and how much tension do I need on the spring to reach this high fps.

Lastly, I would like this gun to be accurate at a minimum of 15m. Would I need a rifled barrel to accurately hit a target at this range? If so, How can rifling be achieved? Aluminum, Brass and Steel pipes are my 3 choices for barrels.

If anyone has a diagram of internals for a commercial spring piston rifle it would be very much appreciated if you can upload it here so I can see it.

Thank you.
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Unread postAuthor: Zeus » Mon Dec 19, 2011 6:54 pm

I have decided to build a Spring Piston Rifle and that is final. They are simple to make and I know how they work.
It is basically a Piston with some O-rings and a Rubber sealing face that is in a tube with a spring behind it.
I Have searched on this forum for a topic similar to this and I can't find one.


They are simple, but the spring has to be very powerful.

I only need a few questions answered.
Firstly, in commercial spring piston rifles, a pellet is fired at around 700 fps using .22 or .177 caliber pellets. How long is the piston and the piston chamber?


I believe the pistons have a stroke of about 4" and the piston tube is about 1 1/4", but I may be wrong.

Second, I will probably be shooting .177 caliber pellets or 4mm Steel Ball Bearings. I want to shoot these projectiles at 650 - 700 fps. How long would my spring have to be and how much tension do I need on the spring to reach this high fps.


That's a lot harder to determine, the spring has to be strong though, I haven't seen many springs around that are this strong.

Lastly, I would like this gun to be accurate at a minimum of 15m. Would I need a rifled barrel to accurately hit a target at this range? If so, How can rifling be achieved? Aluminum, Brass and Steel pipes are my 3 choices for barrels.


Accurate to what? Minutes of watermelon? 10MOA? One ragged hole? Give us some comparison please.

If you look at thehomegunsmith.com, there's a lot of home made rifling machines, it's quite involved to make one.

If anyone has a diagram of internals for a commercial spring piston rifle it would be very much appreciated if you can upload it here so I can see it.


Can't help with that I'm afraid, I'll see what I can do later.

Thank you.


My pleasure.
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/sarcasm, /hyperbole
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Unread postAuthor: Gun Freak » Mon Dec 19, 2011 6:59 pm

Guys guys... How many times have we steered people away from this idea (myself included :D ) ?
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Unread postAuthor: DerpWithAGun » Mon Dec 19, 2011 7:09 pm

Gun Freak wrote:Guys guys... How many times have we steered people away from this idea (myself included :D ) ?


I don't get what you mean. Are you saying Spring Piston's are dangerous? I just hate having to pump up after every shot on my airguns. In my opinion, PCP airguns look ugly because of the large air chamber. Cartridges are too fiddly. It would take hours to construct one so imagine about 20 of them?

Thanks for the info Zeus! :D
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Unread postAuthor: Gun Freak » Mon Dec 19, 2011 8:25 pm

They are dangerous to make because of the forces involved especially when seeking this kind of performance.
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Unread postAuthor: DerpWithAGun » Mon Dec 19, 2011 10:16 pm

Could you please elaborate? What is dangerous about the forces involved? I'm going to be getting a lathe and a mill so wall thickness and creating threaded plugs are no problem.

Guys, What if I used a spring from an airsoft rifle? Airsoft is illegal here in Australia but there are people who customize their springs in order to achieve higher FPS. I'm sure a simple spring would get through customs. I'll look around see what I can find.
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Unread postAuthor: warhead052 » Mon Dec 19, 2011 10:22 pm

Derp, use a gas ram. Much easier to use instead of a spring. Plus you can adjust power unlike a spring, which would require shims and all sorts of stuff.
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Unread postAuthor: Gun Freak » Mon Dec 19, 2011 10:42 pm

Ah, well with a lathe and mill, it's another story! You'll need more than an airsoft spring... Those are wayyyy too weak. They're made for propelling super light plastic projectiles at low speeds. You'll need a stronger spring to get them pellets flying.
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Unread postAuthor: DerpWithAGun » Mon Dec 19, 2011 10:51 pm

Alright then, where could I could a stronger spring? The cocking effort on some airsoft guns is quite hard I've heard. They shoot up to 550 fps. I have shot my friend's commercial spring piston and cocking effort is barely hard. His pellet gun shoots .177 pellets at 700 fps I think. I wonder how hard the cocking effort will be. Break barrel mechanism is too hard for me and requires a welder so I will be doing bolt action cocking method.
With bolt action I may even be able to incorporate a magazine.

I'll have a look on ebay for some Spring Piston rifle repair and spare parts maybe I might find a spring. I was also thinking of buying 3 airsoft springs and putting them together, second thoughts on that now.

EDIT: I don't want a gas ram. It's basically just a pneumatic then. Having to refill the chamber with gas after every shot. No thanks.
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Unread postAuthor: Gippeto » Mon Dec 19, 2011 10:55 pm

X2 on the gas ram. :)

AND... you can build it with the lathe. :D

Trigger bits will be under considerable strain...make certain they are up to the task.

A quick search turns up some interesting results....I KNOW one of these guys. :lol:

http://www.spudfiles.com/forums/home-ma ... t9049.html

http://www.nzairgunners.com/nzairgunfor ... php?t=1880
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Unread postAuthor: DerpWithAGun » Mon Dec 19, 2011 11:26 pm

I understand how it works. There is 2 major factors of the gas ram that make me say "I'm not doing it."

Firstly, You must recharge the gun with air after every shot. This is what I've been trying to avoid all along. The air from the chamber will be released quickly into the piston's chamber and then it will send it flying, propelling the projectile. The air wont stay permanently inside the chamber as it can cause damage to the gun's internals and the air will just escape past the trigger mechanism.

Secondly, This gun requires the use of a ball valve. Ball valve...... Ball valve.... This word makes me want to puke. It the most ugliest part to use for an airgun I have ever seen. And If I'm going to undergo this gas ram I might as well just make a ball valve air gun. Now you will say, make a homemade valve. Complicated and it requires a double cock. I must cock the piston to the trigger so it doesn't slide around inside it's chamber then I must cock the valve inside. To make one cocking stroke cock a valve and a piston at the same time is very complicated and not compact.

This is just my understanding of a Gas Ram. What I have said here maybe completely wrong and none of this is a Gas Ram. I read JSR's post in the link provided by Gippeto and from the diagrams in the thread, it contains a Ball Valve.

Someone please explain this Gas ram to me further.
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Unread postAuthor: Hawkeye » Mon Dec 19, 2011 11:27 pm

They are simple to make and I know how they work.... so can you guys tell me how they work and show me how to make one? :lol:
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Unread postAuthor: DerpWithAGun » Mon Dec 19, 2011 11:30 pm

It doesn't say show me how to make one it says please explain FURTHER
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 20, 2011 12:35 am

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Unread postAuthor: DerpWithAGun » Tue Dec 20, 2011 1:27 am

Thanks for the info JSR, I read through everything carefully and I've actually thought of a pretty neat idea.

I'm going to design it without a spring.
It will have a very long piston inside that will be hollow. There will be an O-Ring right on the back of the piston, an O-ring in the middle of it and then a sealing face on the front. There will be a schrader valve behind the piston's chamber. I will pressurize the chamber to 100 psi for testing and maybe a maximum of 1000 psi. The wall thickness of the chamber will be 2mm. My hopes for this design is that, you only need to pump the gun up once to 1000 psi before you go to shoot. All of the holes in the piston and piston chamber that are used for the trigger and cocking the gun will be moved forward past the second O-ring. Because the piston will be long and have multiple O-rings air will not be able to escape anywhere. You cock the piston, add a pellet and fire away. After you finish shooting You get a rod and press it into the schrader valve which will release all the air. This will prevent any damage when the gun is stored. Now when you want to shoot again just pump it with air.

This wont be a complicated design. I'm not going to have any fancy bolt action style loading. It will just be a lever beside the piston. I will just pull it back, load a pellet and push it forward. I'm going draw some designs and do some calculation into GGDT. I would enter the size of my chamber, the weight and size of my piston and the amount of pressure. Then I would get an FPS count of it and with some use of Google I'll find a conversion table to convert FPS to MPH. If it reaches 70 MPH then this gun will easily shoot a pellet at 800 fps.
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