Spring Piston Air Rifles

[maverik94]

Ok, I am interested in possibly making one of these guns, they are calles Spring piston guns. Essentially, this is how your typical commercial Crossman or Ruger or Gamo air rifle works I believe. (Corect me if I'm wrong) Anyway, I found an article about this kind of gun here, http://www.pyramydair.com/blog/2008/12/ ... works.html Would this gun be at all powerful? Do any of you know where I can read more about this type of gun? Also, does anyone have any experience making one of these? I have looked a bit on Google and found little. Thanks Yall!

[sputnick]

Good luck, all I have to say.

Its possible, but with just plastic you will end up with a POS gun.

I would imagine it would be near impossible to do unless you had decent metalworking skills, and experience making air rifles.

[Ragnarok]

Essentially, this is how your typical commercial Crossman or Ruger or Gamo air rifle works I believe.

It's very common for air rifles to work in such a manner, yes.
If you're picking up an air rifle for not too much, it's almost certainly either a springer or CO2 powered.

Of course, they need not be particularly cheap either. I own an Air Arms TX 200 HC, which uses a spring piston and which goes for $570 and upwards on Pyramid air.
In my case though, I paid the equivalent $625 for mine. Kind of daft, given I live in the UK, so I didn't even have to pay any kind of import fees (Air Arms is a British company).

Very nice rifle though. I'd give it a recommendation to most people.

Would this gun be at all powerful?

As I understand it, practical limits are about 40 ft-lbs muzzle energy. After that, the springs get too large and powerful to be cocked by most people.

Also, does anyone have any experience making one of these?

Yes. It cost me a very large chunk out of the side of my left forefinger, and the spring I was using was a mere fraction of the strength of the one my Air Arms needs to achieve just 12 ft-lbs.

Generally, I advise people not trying to build spring piston airguns themselves for those very reasons - they've got very powerful springs for even reasonably modest muzzle energies - and unless built well, you're at risk of trapping fingers in things, or having the whole thing fly violently apart.

Indeed, my accident with the construction of a springer was the main reason I chose the TX200 over the similar Weihrauch HW97K. The Air Arms has a built in "anti bear-trap catch", which although some people find it annoying, dramatically reduces the potential for having your fingers cut off or mangled when loading - if the compression tube and mainspring should come loose during loading, they're not going to be polite to fingers in the way. (That's why it's known as an "anti bear-trap". Because it stops it springing shut on your fingers.)

Of course, if you have the skill to come up with a reasonable design and want to build something low powered for nerf darts/airsoft BBs, or have the potential to machine parts for a more powerful version, and most importantly can avoid the temptation to play around with "incomplete test models" that have exposed moving parts... then don't let me stop you.

But generally, it's low powered, and hard to make, so it's not normally something most people want to go to the effort of doing.

[hi]

Yes, they are extremely simple, but making a trigger mechanism for them is very hard without the right tools. The one I have is made out of steel, probably due to the stress that is put upon the frame when it is cocked and ready to fire.

[jackssmirkingrevenge]

But generally, it's low powered, and hard to make, so it's not normally something most people want to go to the effort of doing.

As often stated on this forum, couldn't agree more. If it's power you want, unless you're John Whiscombe, don't bother. On the amateur level most spudders operate, it is countless times easier to build a powerful pneumatic or combustion than it is a spring piston airgun, what you'll end up with will doubtless be less powerful than a cheap airsoft pistol.

This is the closest I ever came ten years ago, never made a springer since.

[Ragnarok]

If it's power you want, unless you're John Whiscombe, don't bother.

Darn, I meant to mention Whiscombe rifles. It completely skipped my mind.

I also completely forgot to mention that in spite of losing part of a finger, performance was atrocious to add insult to literal injury.
It's not really a good path to try and explore. Fine commercially, but not for the average spudder.

[Technician1002]

Yes, they are extremely simple, but making a trigger mechanism for them is very hard without the right tools. The one I have is made out of steel, probably due to the stress that is put upon the frame when it is cocked and ready to fire.

I like your sig. I was just thinking the hardest part would be the engineering for efficient energy transfer.

Releasing the spring changes potential energy to kinetic energy to the piston and projectile. The piston kinetic energy should be efficiently transferred back to potential energy in compressed gas in the barrel. The right sizes and energies needed for efficient transfer here needs engineering skill. Too little transfer and you will need a bumper instead of just the air compression. Too much transfer and the piston recoils off the air and doesn't achieve max transfer to the projectile.

Tuning it for spring, mass, volume, projectile.. It is rocket science to get peak performance.

[jackssmirkingrevenge]

Tuning it for spring, mass, volume, projectile.. It is rocket science to get peak performance.

There's also the point that a lot of the energy comes from the diesel effect where some of the lubricant in the piston chamber actually ignites. I believe Gerald Cardew had done some experiments with spring piston airguns fired without lubricant - ie removing the possibility of ignition - and power was significantly less.

edit: morning lapsus

[Technician1002]

Tuning it for spring, mass, volume, projectile.. It is rocket science to get peak performance.

There's also the point that a lot of the energy comes from the diesel effect where some of the lubricant in the piston chamber actually ignites. I believe Gerald Cardew had done some experiments with spring piston airguns fired in a vacuum - ie removing the possibility of ignition - and power was significantly less.

Spring piston valves are missing the energy transfer from kinetic (piston motion) to potential (compressed air) since the air is removed in a vacuum. Removing any component including air removes part of the energy transfer path.

[jackssmirkingrevenge]

Spring piston valves are missing the energy transfer from kinetic (piston motion) to potential (compressed air) since the air is removed in a vacuum. Removing any component including air removes part of the energy transfer path.

*blink*

Right you are, that should have read that the experiment was indeed lubricant, not air, free - corrected.

[Ragnarok]

Actually, I've taken to just using silicon lubricants in my air rifle, because they can't diesel like the petroleum based ones.

Makes maintenance less fussy, because I don't have to be so precise over where I'm getting the stuff.

[SPG]

Actually, I've taken to just using silicon lubricants in my air rifle, because they can't diesel like the petroleum based ones.

Makes maintenance less fussy, because I don't have to be so precise over where I'm getting the stuff.

Me too, everything I ever read as a youngster mad keen on air-rifles told me that dieseling was a bad thing, resulting in poor consistancy and damaged seals. Of course it didn't stop me trying it in my old BSA Scorpion air-pistol (how I wish I still had that).

Lets not forget though that the basic spring-piston idea is used very successfully in almost every airsoft gun, whether cocked by hand or by electric motor.

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[Ragnarok]

Of course it didn't stop me trying it in my old BSA Scorpion air-pistol (how I wish I still had that).

Oh, it happened a few times by accident with my TX. It's why I swapped to non-combustible lubricants.

Lets not forget though that the basic spring-piston idea is used very successfully in almost every airsoft gun, whether cocked by hand or by electric motor.

It might be, but those are made from parts which they have the facilities to make almost any shape, and they only need muzzle energies of perhaps 2 joules at most. Making one by hand would still be a challenging task, and offer little actual power.

[john bunsenburner]

Back on topic: Perhaps what you could do is construct some kind of air spring instead of a metal one, that can eb made ajustable and works very well. Its also less dangerous that your average mechanical spring. I persume the others woudl agree that using n airspring would most probably end with an idea that is some what safer and easyer than the orginal one while the concept really stays the same.

[maverik94]

Even though most of you think it's a bad idea, I think I am going to go ahead with this project. (Ragnarok I will be careful). John, funny, I had that same idea on the way home from school, but It will be hard to seal it with a trigger mech. I think I'm going to start by making a small prototype. Im thinking a 1' length of 1 1/2" pvc as the chamber. Then a piston that fits snugly and is sealed with multiple o-rings. Dieseling... doesnt sound too safe, I will try to use silicone based lubricants...like? Im thinking a 5/16" barrel. One last question: What's the best way to attach a 5/16" barrel to some 1 1/2" chamber STRAIGHT? Do they make flat pvc caps or something? Thanks Yall!