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Spring Piston Air Rifles

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Ragnarok » Tue May 05, 2009 2:43 pm

maverik94 wrote:Even though most of you think it's a bad idea, I think I am going to go ahead with this project.

Seriously, you're going to put in a lot of effort and money for not a lot of end result. It's almost certainly really not worth it.

Go ahead if you're really really REALLY set on it, and you're totally convinced that it's the right thing... but I'm fairly confident that you'll be disappointed in the end.
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Unread postAuthor: sputnick » Tue May 05, 2009 2:49 pm

Ragnarok wrote:Go ahead if you're really really REALLY set on it, and you're totally convinced that it's the right thing... but I'm fairly confident that you'll be disappointed in the end.


Agreed, my brother undertook a project like this, with cpvc, but instead of a spring, he used a long pipe and bungee cable, I helped him wherever I could, (he's only 12) but neither of us could make a decent seal, or trigger mech.

To be fair though, we did give up fairly soon, but still, be prepared for a frustrating ordeal of failure.
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Unread postAuthor: jackssmirkingrevenge » Tue May 05, 2009 3:07 pm

I have no doubt you can make one which works, however I'm confident that in terms of power it will be negatively disproportionate to all the effort you've put into it. If however you want to make something of mechanical interest with no regard for performance in terms of muzzle energy, why not :)
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Unread postAuthor: maverik94 » Tue May 05, 2009 5:11 pm

I dont see why it will be so weak. If I have a 1 1/4" chamber, 1' long, and a 5/16" barrel, the reduction in the volume will be so huge it would generate quite a bit of power. At leat that's the way I see it. Also, my prototype will not take a lot of work, there will be no trigger mech, just a manual pullback. All I need yet, and maybe yall can help me, are these things are:
http://www.spudfiles.com/forums/viewtopic,p,243130.html#243130

and http://www.spudfiles.com/forums/viewtopic,p,243131.html#243131
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Unread postAuthor: jackssmirkingrevenge » Tue May 05, 2009 10:03 pm

maverik94 wrote:I dont see why it will be so weak. If I have a 1 1/4" chamber, 1' long, and a 5/16" barrel, the reduction in the volume will be so huge it would generate quite a bit of power. At least that's the way I see it.


I have one of these, recently I had to change the spring and it was quite a chore. As you can see from the attached pics it's a massive affair and with lots of preload, if fact there's no way you could preload it manually by pulling, let alone cock it - this is why most springers use some sort of lever mechanism.

Even with all this stored energy, it only manages 4.5 ft/lbs of muzzle energy. This is equivalent to chucking a 100 gram slug of potato at a mere 35 feet per second, something which even the most basic combustion will achieve with no effort whatsoever.

You can imagine therefore what sort of power you'll get for something which can be cocked manually. Well, of course you can. Airsoft pistols ;)
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Unread postAuthor: inonickname » Tue May 05, 2009 10:25 pm

The people here are correct; power will be rubbish. Even to push 100 psi the spring will have to put in the same amount of power you would (100 lbs/in^2). This is a very powerful spring, and will require a lever or reduction method such as a thread to recock.

Then add to that you need a trigger mechanism and strong seals with minimal friction, power will be junk.

If you decide to even try, a compressed gas piston is the only way I can see this working.
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Unread postAuthor: LeMaudit » Tue May 05, 2009 10:59 pm

You need to carefully think of a way to keep safely compressed a powerful spring like that. I had the same idea not so long ago, but it was all metal, not PVC. And my spring was smaller and compressed with a thread. I understand PVC is brittle, and a repetitive shock from a powerful spring could be very dangerous IMO.

Also, I quickly forgot about that idea, because a spring that is manageable in term of size and power would not be enough to be very impressive. I did some math computation with spring rates from McMasterCarr, and the result was bad. I think what I intended to do first would have just resulted in a glorified cork gun :-D That's also a lot of fun though!

I believe to have a decent power from a spring rifle (and I do own a Diana model 35 that is a fine rifle), you need to do metal construction, finely tuned, and you can't expect launching much more weight than half a gram (8 grain) which is a .177 pellet.

This is why I finally prefer PCP (precharged pneumatic, not angel dust for those who are still confused ;-) !). And this of course also have its share of potential danger. But as other said, a spring is quite dangerous. I remember working with a small one for a project (2 inch long, 1/4" diameter), and after just a second of inattention it poked my eye and I would certainly look like a french pirate now (remember inspector Clouseau, with a parrot on his shoulder?) if I didn't had my workshop security glasses.

Of course I'm just a beginner here, but please follow advices from experienced people. Jackssmirkingrevenge, Ragnarok and others seem to know quite a lot on the matter. Even with my machinist experience background I would follow their advices, or at least very seriously consider them.

Have fun, and be safe.
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Unread postAuthor: Ragnarok » Tue May 05, 2009 11:08 pm

jackssmirkingrevenge wrote:This is equivalent to chucking a 100 gram slug of potato at a mere 35 feet per second, something which even the most basic combustion will achieve with no effort whatsoever.

You could throw potato faster than that.

My 0.6J airsoft shotgun can just about have it's mainspring cocked by the rather infeasible "one-handed pump" method (you know the kind of thing), but it had to have extra weight added to the body and it still takes practise and sheer violence to do it.

Looks damn cool though.

There'd be no chance of doing it with my air rifle though - aside from the fact that it doesn't have a pump. In fact, on that note, you never see any springer more powerful than a airsoft gun being cocked with a pump action - which should give you an idea of the spring forces that are needed for relatively small muzzle energies.

Although disassembling my Air Arms is no great chore to manage, the TX is renowned for being very easy to maintain, and for being able to be disassembled or reassembled without any form of spring compressor. But even then, I still need to put the muzzle of the rifle down on some carpet and put a lot of weight on the trigger block when taking it apart/putting it together.

Without putting my weight on it, the task would be pretty unattainable - taking an end of the mainspring between each palm, it'd be an exceptional person who could compress the two ends much more than half an inch together.

The forces on it when it's actually compressed and cocked in the rifle - like I said, if it came loose when my hand was in the way, I would find myself without a large amount of finger, and I'd have to start to learn to write left handed.
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Unread postAuthor: jackssmirkingrevenge » Wed May 06, 2009 12:05 am

Ragnarok wrote:You could throw potato faster than that.


Since the energy to cock the spring is coming directly from a single stroke of the arm, that makes perfect sense.

Ragnarok wrote:My 0.6J airsoft shotgun can just about have it's mainspring cocked by the rather infeasible "one-handed pump" method (you know the kind of thing), but it had to have extra weight added to the body and it still takes practise and sheer violence to do it.


Try as I might, it's hard to picture you being bad-ass while doing that :D
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Unread postAuthor: Ragnarok » Wed May 06, 2009 12:34 am

jackssmirkingrevenge wrote:Try as I might, it's hard to picture you being bad-ass while doing that

That would imply that I'm not bad-ass all the time...
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Unread postAuthor: jackssmirkingrevenge » Wed May 06, 2009 1:15 am

Ragnarok wrote:That would imply that I'm not bad-ass all the time...


And that you'd be bad-ass in a school shooter sort of way as opposed to a terminator sort of way...
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Unread postAuthor: Ragnarok » Wed May 06, 2009 1:43 am

Well, darn. I must have put my bad-ass down somewhere then. I'm terrible at losing things.
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Unread postAuthor: maverik94 » Wed May 06, 2009 2:32 pm

okok, I get it. This gun will suck. But then how do commercial air rifles shoot .177 slugs at 1200 fps?
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Unread postAuthor: Ragnarok » Wed May 06, 2009 2:58 pm

maverik94 wrote:But then how do commercial air rifles shoot .177 slugs at 1200 fps?

Very very powerful mainsprings - and often, quite a bit of overgenerous marketing. It's rare to actually see an air rifle make the velocity it's marketed as capable of.

My air rifle is only good for about 800 fps, but even then the rifle has to be built like a tank to contain the spring. To give you a comparison, it weighs more than most fully loaded assault rifles.
Seriously. An M16 with a full 30 round magazine weighs about 4 kilos. My TX 200 weighs in at around 4.7 kilos - well, technically, it's 4.2 kg without the scope, but it's got no built in sights, so it can't be used without a scope, so for functional purposes, in working order, it weighs 4.7 kg.

It also needs a big mechanical advantage to make it possible to cock it. That's at 800 fps. 1200 fps rifles need to be built tougher and with stronger springs.

You should also consider the energy in a 1200 fps 8 grain .177 pellet is only 25.6 ft-lbs, not a very large amount (although it could still kill a person if they were rather unlucky).
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Unread postAuthor: maverik94 » Wed May 06, 2009 3:12 pm

yeah, so it is possible, I'm still gonna try this....
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