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Spring-Piston Size?

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 Size?

Unread postAuthor: mark.f » Mon Jan 22, 2007 7:21 am

This really belongs in an airgun forum, but seeing as the one I tried to register on still hasn't let me in with my username and password, I figured I'd ask here and see what a few of you had to say.

What would be the minimal size of the piston on a spring-piston airgun shooting a .177 caliber pellet through a barrel 24" long? I believe you can go as high a volume as you feel like, but I'd like to know the minimal volume. The pellet would move at a certain pressure regardless of how much volume the cylinder would displace, so I guess after that it's simply a matter of the piston having as much or more volume as the barrel?

So, I guess the root of this question is what's the static friction of a pellet in a rifled airgun barrel? From here, I can pretty much determine the size piston you would need for a certain barrel.

Thanks,
Mark
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Unread postAuthor: Copperboy » Fri Jan 26, 2007 8:35 am

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Unread postAuthor: mark.f » Fri Jan 26, 2007 11:49 pm

Very interesting link. I had a good time viewing his plans and pictures. Very nice work.

BUT, we're dealing with pellets in a rifled barrel here. I believe the static friction of the projectile has a lot to do with it, and a pellet is much more stiff than a dart in 1/2" CPVC. If a pellet can hold back around 30 PSI of air, then the piston needs to displace enough air to keep a pressure of at least 30 PSI up to the end of the barrel.
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Unread postAuthor: judgment_arms » Sat Jan 27, 2007 12:18 am

I click on this topic expecting that my knowledge of springers would be helpful, I was wrong… 24inch barrel on a pellet gun? I’m guessing your making your own air rifle. what kind of performance are you looking for? Where are you getting a 24inch barrel? I guess I’m not being much help… I’ve got a few springers, would dimensions from them be any help?
Go on the Crosman Airgun Forum and/or the Yellow forum and ask for “Steve in NC”, he knows a LOT about the physics involved in air rifles, if anybody knows the answerer to you question he does.
Sorry I can’t be more help Friend.
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Last edited by judgment_arms on Sun Jan 28, 2007 3:15 pm, edited 1 time in total.
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Unread postAuthor: Mr.Russ » Sat Jan 27, 2007 12:32 am

anyone know how that gun is powered? and if its powerful enough to shoot a marble/bb?
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Unread postAuthor: judgment_arms » Sat Jan 27, 2007 12:52 am

Ahhh, the F.A.R. I’ve studied that gun for hours upon hours. It’s powered by an “AR15 main spring”, marbles may be a bit too heavy, but if you used it like a scattergun with the shells full of BBs it should be interesting. If you go to make this the “AR main spring” he’s talking about is actually the AR’s buffer spring; the main spring is about two inches long and about half an inch in diameter, if my memory serves…
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Unread postAuthor: Mr.Russ » Sun Jan 28, 2007 6:52 am

ohhh... is there any way to convert it to air?
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Unread postAuthor: mark.f » Sun Jan 28, 2007 9:39 am

judgment_arms wrote:I click on this topic expecting that my knowledge of springers would be helpful, I was wrong… 24inch barrel on a pellet gun? I’m guessing your making your own air rifle. what kind of performance are you looking for? Where are you getting a 24inch barrel? I guess I’m not being much help… I’ve got a few springers, would dimensions from them be any help?
Go on the Crosman Airgun Forum and/or the Yellow forum and ask for “Steve in NC”, he know a LOT about the physics involved in air rifles, if anybody knows the answerer to you question he does.
Sorry I can’t be more help, Friend.

Actually, I'm not making an airgun. I was interested in trying an idea of mine on combining a gas-spring air rifle and a pump into one. Sounds weird but trust me, it's not that oddball.
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Unread postAuthor: CpTn_lAw » Sun Jan 28, 2007 9:57 am

that doesn't sound weird at all, basically, you could do a gun with the springer mechanism, of any caliber you want it to be, just put a adequate force behind the piston to compress the air as fast as possible, and a good retaining device for your projectile, in order to maintain it as long as possible, to give the piston enough force to compress the air before the projectile goes.

Oh, regarding the pressure you need to apply to the pellet for it to be forced in the barrel, is approx 8 bars and up. CO2 pellet guns, use a hammer valve that release a small container of CO2 per shot, which is at 9 bars. again, it is CO2 pressure....
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Unread postAuthor: judgment_arms » Sun Jan 28, 2007 2:32 pm

Mr.Russ wrote:ohhh... is there any way to convert it to air?

No Mr.Russ, there’s no easy way to convert it to air. Google boltsniper (the guy that made the FAR, it should pull up his website.) he made a pneumatic, well actually it’s Co2, NERF gun on a similar feed principle, two actually, one a bolt action the other automatic.

CpTn_lAw, where did you hear that? Not saying your wrong just I would like to know.

Mark, your idea isn’t crazy, its sounds a lot like the Theoben gas ram. I’m interested in knowing more, unless it’s classified, and where are you getting your 24inch .177cal/4.5mm barrel? I was not aware such a thing existed
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Unread postAuthor: CpTn_lAw » Sun Jan 28, 2007 2:53 pm

Be more specific please. Where did i hear what?
The pressure of the co2 that pushes the pellets , i got this from a french forum, i was searching for this information for a few hours to answer to mark.
For the "everything can be fired out a spring piston" thing, it is physics. If you keep the ratios proportional to a conventionnal springer that shoots pellets, -and by that i mean, everything that counts.- you just transpose it to your barrel dimension, you just need to be a bit clever to elaborate this.
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Unread postAuthor: judgment_arms » Sun Jan 28, 2007 3:06 pm

Yeah, sorry CpTn_lAw, I meant the thing about Co2 guns. But you still answered my question, thanks
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