Air Guns

[Sako]

Hello everyone
I’ve been planning to build an air gun for some time now, and I have access to a machine shop once again.

I was wondering what is best, a spring-piston gun or a pre-charged pneumatic?

Spring-piston air guns look to have fewer parts and less accurate parts than a pre charged gun, making it easier to build.

Does pcp’s have any advantages besides multiple shots?
Multiple shots would be nice but I’m planning on using 250 psi. so I don’t think I would get very many shots off that.

If I was to go with a spring-piston gun, how powerful should the main spring be?

Thank you for any help


[This message has been edited by Sako (edited September 20, 2001).]

[Agent Blak]

PCP is good for the Superman like high, almost nothing can put you down. it is the who;e reason for the invention of "non-lethal weapons."

------------------
A wise man once said:
"...There Will Be No
Stand Off At High Noon
... Shoot'em In The Back
And, Shoot'em In The Dark"

Agent Blak-------OUT!!

[zaibatsu]

You've forgotten whats the easiest (imo) type of airgun to make - the pump-up pneumatic. I'd post more on this, but don't have the time at the moment, I'll post more later if you want.

250psi isn't going to do a lot, I'd say use a pressure of around 500psi, in .22 calibre, with a 20" barrel, that should give you around 12ftlb, more if you used a heavier pellet. I'd say is you could make something that could stand these pressures, then a resevoir capacity of 1"^3 with a pressure of 1000psi would be best, as it would give a high power of 26ftlb.

Pump-Up Pneumatics are pretty easy to make I think, I've finalised my design for one, and it doesn't look to have a lot of different parts, and those that it does have are easy to machine.

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[Sako]

The only problem I can see with using 500 psi. is how can I get such pressure?
I’ve seen small compressors that will pump up to 250 psi. and that’s the highest I’ve seen.
May be I will use a paintball gun tank as a reservoir.

Zaibatsu- can you please post your information?

Pump-Up Pneumatics, how much pressure does the pump produce?

[zaibatsu]

Right, pressure of the pump...

Here is the formula you use - P1V1=P2V2.

So, if we want to fill a reservoir with volume 1"^3 with 1000psi, then we already have P2(1000psi) and V2 (1"^3)

We also know P1, as its just air at standard pressure, which is around 14.4psi. so we also now have P1, so to find the volume of air we need to compress to fill a reservoir of 1"^3 with 1000psi of air = 1000/14.4
=69.44444444444

So, we need to compress 69"^3 (to 2sf) of air. We could either have a small diameter pump-cylinder thingy combined with a long stroke length, or a large pump-cylinder combined with a short stroke.

However, this 69"^3 can be done in many short strokes, or a few very heavy strokes. So basically just mess around with the amount of strokes you'd like, pump-cylinder diameter, and stroke length till you get the ratio you want. Bear in mind it'd be better to start off at a small pressure like 500psi, although that'd only give around 16ftlb in .22 cal with a 21gr pellet in a 20" barrel.

Its late, this is probably full of mistakes, anyone feel free to correct me, I need sleep.

------------------
Handguns don't kill people... Half as well as full-auto
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[Sako]

Thank you for the information

[BoB-]

I had this weird dream,

in it, I got lethal (a very large rabbit) results using a .22 barell, using only 70psi. The difference was my chamber volume, I used a 12" long 3/4" diameter galvanized steel chamber, using a small handpump bought at walmart, I could get 80psi in 20 pumps.

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Teamwork is essential.
It lets you to blame someone else.

[BoB-]

You mentioned spring pistons, can anyone tell me how they work? I would be very grateful.

------------------
Teamwork is essential.
It lets you to blame someone else.

[zaibatsu]

BoB- you will know what a spring piston airgun is, although the name might not ring a bell. Spring piston airguns usually have three methods for cocking (break-barrel, underleaver and sideleaver) and they compress a spring.

The piston is in front of the spring, and when the spring is compressed, it is held back by the trigger mech. When the trigger is pulled, the piston is released, letting the compressed spring force the piston forwards, compressing the air and pushing it through the air port. Also, there is a process called dieseling going on, this goes on in most airguns, and is not really a negative thing, but over dieseling is. Basically the lubricants ignite due to the high pressures and temperatures, and this gives the gun more power.

They're pretty simple guns to keep working, less fiddly than a PCP or Pump-Up pneumatic, and are cheaper to buy (usually).

------------------
Handguns don't kill people... Half as well as full-auto
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[Anthony]

The peak chamber pressure produced by a spring/piston gun with 12ft/lb muzzle energy is about 1000psi.

It's funny you say that BoB-, I had pretty bad results using a 36" barrel, 36" 3/4 air chamber and .22 pellet at 100psi. Power was considerably less than 12ft/lb air rifle. But with a 0.50" barrel and 350gr slug it'd do about 90ft/lb

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"Shit happens. Get a fucking helmet"

[Scientist]

You've forgotten whats the easiest (imo) type of airgun to make - the pump-up pneumatic. I'd post more on this, but don't have the time at the moment, I'll post more later if you want.

Please post it. Thanks.

[MMIV]

there are good looking air gun designs in the makeshift arsenal (aussie owned!!) one air gun has a air camber behind the barrel which is charged with a bike pump and a air tap valve is used to discharge the round. the other design was that a aerosol can was attached to rear to discharge to projectile but i was thinking of replacing with co2 canister used to pump bike tires.

what are your comments about this idea, anyone??

[A2675770]

From my own exprience, I took a 1976 crackbarrel 1 hand pellet gun and turned it into a high pressurized dart gun.
The similarities (from a basic semi-auto paintball gun, Where I got the idea) after removing the spring, is pure insanity. I simply bored out the barrel to fit the proper darts (not exactly sure of the total diamiter off the top of my head)
Drilled and tapped the back of the barrel 3/4, and socketed in the tank attachment.
With a nice 20oz tank, it had surprising acuracy, up to 150-200 yards,
Only problem was the single load darts, I wish I could have thought of a way to custom some kind of rigged up clip :\ .

-A26

[Macgyver]

Wouldn't this be something more fun to build?

http://www.burntlatke.com/bb.html

A BB machinegun..... At least some pieces of the design found on that link can be used, but I'd prefer to use a portable pressurized gas container rather than having a hose connected to an air compressor.

Perhaps a paintball CO2 tank or something similar?

[xperk]

Sako,

I would certainly go for a pcp design as this would give you max power in a controllable envelope.
Spring powered airguns are hard to control once they get beyond a certain power limit while pcp's are surrealistically sweet.
People go bear hunting with pcp's.
.50 can be done with a pcp.

For inspiration take a look at:
http://www.barnespneumatic.com/

Most pcp shooters invest in a divers tank to fill their guns - refill of the tank is relatively cheap.

[FragmentedSanity]

Im quite intersted in pump up penumatic air guns. Ive long believed them to be entierly underated. The ability to charge the air chamber any where - without bulky equipment - as many time as you want has some definite advantages. Sure the time between shots is much longer, but that just teachs you to shoot straight the first time!

Id be intereted in any info or pics anyone has. There is a simple pistol version in the PMJB Vol 3 - page 52. Ive wanted to make something along those lines for a while now. Any comments or suggestions would be welcomed.

[Spoz]

In regards to how you are to get a pressure of 500psi, I suggest CO2. Carbon dioxide is cheap and readily available in canisters for paintball or even soda stream chargers. at 25C it will have a pressure of around 830psi from memory, and will go up to 1000psi or so on a hot day. This would kick ass in a small caliber rifle, I designed a .177 caliber rifle that would be semi automatic and should be reliable, I just do not have a lathe to make the parts :(

If you want to stick with low pressure simply increase the barrel diameter, it means less force per square inch is needed but you need a higher volume to compensate, hence making them larger. I have a cannon that achieves 100m/s at 80psi, the barrel size is 1". Its quite bulky, but will shoot a 700 gram steel slug through several inches of hardwood, with a recoil to match a .30-06 at higher pressures. Great for backyard fun.

[xperk]

FragmentedSanity,

Some url's you may find interesting:

Commercially available model:
http://www.straightshooters.com/ourtake/otr9mm.html

History of pneumatic guns:
http://air.guns.20megsfree.com/
(note the black powder conversion in the vintage section)

[FragmentedSanity]

Thtas the kind of thing im talking about... and if I could buy one I would. but im reduced to trying to make do with what I can make. but one would think that if they could be made in the 1600s we should be able to do it know without too much hassle...
quoted from sites linked above.

There was even a Elite Unit in a Austraian Army that carried .36 cal. and .51 cal. Air Rifles that shot up to 20 rounds with one charge, at speeds up to 1,000 fps .... A Austrian Miltary Air Rifle designed by Grandoni in 1779 shot 20 rounds of .51 cal. bullets at speeds as high as 1,000 fps on one charge.


thats fairly impressive.

Me _ I just want something simple - I dont care if I have to charge it every shot - just a nice powerful big bore air rifle., and a pistol for plinking.

thanks for the links anyway.

[Third_Rail]

I've been using a CO2 setup, myself.

Using dead-soft .36 caliber lead roundball, I get 600-700 fps. I'm pretty happy with it, overall, but the trigger mechanism has to be improved. Currently I'm just using a modified trigger out of a Crosman pellet rifle, which I'm not happy with.

Does anyone know a better trigger mechanism, or plans for one? I've been having fun with a machining course, and I'd love to make a new trigger mechanism, but I have no plans.