Pellet Gun Barrel Help

[ave210knife]

I am planning to build a 3/4 inch piston valve pellet gun, but I have a few questions regarding barrel size and ammunition. Although I have built a piston valve before I have never build a small one only a 2 inch one.

•What are some different projectiles and corresponding barrel diameters that would be good for a 3/4 inch piston valve?

•My local hardware store has a section of brass tubing in small diameters which would make decent barrels. They are not threaded on the ends so how would I connect it to the threaded output of the valve?

•Would 120 psi from an air compressor be sufficient for decent velocities or is a fridge compressor necessary?

[jackssmirkingrevenge]

•What are some different projectiles and corresponding barrel diameters that would be good for a 3/4 inch piston valve?

What are you trying to achieve? Accuracy at long range, point blank devastation? What makes a projectile "good" is subjective, so it would help to know what sort of results you expect.

•My local hardware store has a section of brass tubing in small diameters which would make decent barrels. They are not threaded on the ends so how would I connect it to the threaded output of the valve?

http://en.wikipedia.org/wiki/Compression_fitting

•Would 120 psi from an air compressor be sufficient for decent velocities or is a fridge compressor necessary?

A large bore gives you decent power for relatively low pressure.

Here is a 3/4" pneumatic I had made: http://www.spudfiles.com/pneumatic-cann ... c7173.html

At 110 psi it blew a marble straight through a large coffee can full of water:



Using the same pressure for something like a 1/4" bore will likely leave you disappointed though.

Again it boils down to what you want to achieve.

[ave210knife]

Fist off, I would like to say thanks for your help. I think that a larger bore at close range is better for my situation. Also I cannot use glass marbles because with my luck I would end up with broken glass in my foot. Although I do have some 1/2 inch ball bearings laying around that would pack a punch.
Once again, thanks!

[jackssmirkingrevenge]

Fist off

Either a typo or it's some sort of fisting competition

I think that a larger bore at close range is better for my situation.

You might want to go for a full 3/4" bore, used CO2 12 gram capsules fit exactly and make interesting projectiles:

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You can also fit 12 gauge shotgun wads (or make your own) to fire multiple projectiles.

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Moar holes is better than one

[ave210knife]

Luckily, that was a typo!

Those CO2 capsules look crazy destructive, but sadly I have no access to any empty ones. I think that I would be better off doing a 1/2 inch bore and using fishing sinkers for ammo.

Is it possible to make a barrel sealing piston valve gun in all copper (with minimal brass parts if necessary)? I would want to make something like in wyz2285's piston valve tutorial but with a 3/4 inch copper tee. I would use a washer piston and a spring so I can fill from the air chamber. I am just a little confused on where the spring would seat on. What could I put in the pipe so the piston is pushed back forwards by the spring, but does not impede airflow?

[jackssmirkingrevenge]

Is it possible to make a barrel sealing piston valve gun in all copper (with minimal brass parts if necessary)? I would want to make something like in wyz2285's piston valve tutorial but with a 3/4 inch copper tee. I would use a washer piston and a spring so I can fill from the air chamber. I am just a little confused on where the spring would seat on. What could I put in the pipe so the piston is pushed back forwards by the spring, but does not impede airflow?

I would recommend a commercial QEV. They care cheap, efficient and save a lot of effort and heartache with piston experimentation.

Plenty of all copper guns for inspiration, here's a few to come up from a quick search of the forum database:

http://www.spudfiles.com/pneumatic-cann ... 25204.html

http://www.spudfiles.com/pneumatic-cann ... 24227.html

http://www.spudfiles.com/pneumatic-cann ... 24060.html

http://www.spudfiles.com/pneumatic-cann ... 22432.html

http://www.spudfiles.com/pneumatic-cann ... 19169.html

Copperhead prime stands out as a particularly neat and well made example: http://www.spudfiles.com/pneumatic-cann ... c6013.html

[ave210knife]

Thanks. Is there any major difference between these two QEVs besides appearance? The black QEV has BSPT thread but the silver one has NPT. Would it be possible to put NPT pipe into the BSPT fitting (NPT is the standard in my country) ?

http://goo.gl/M1Lh9m

http://goo.gl/4KYc6u

[jackssmirkingrevenge]

NPT and BSP are sometimes similar but *not* the same:

While NPT threads are common in the United States, BSP threads are widely used in many other countries.

WARNING: Never, never try to mate a BSP fitting with an NPT or NPS fitting if the pressure holding capability is at all critical.

NPT/NPS and BSP threads are not compatible due to the differences in their thread forms, and not just the fact that most diametrical sizes have a different pitch. NPT/NPS threads have a 60° included angle and have flattened peaks and valleys (this is a Sellers thread form); BSP threads have a 55° included angle and have rounded peaks and valleys (this is a Whitworth thread form).

[ave210knife]

Ok thanks for warning me!