penetration velocity

[chucker]

Does anyone know roughly what velocity would put a 1/2 marble through a groundhog, or atleast kill cleanly. I'm thinking around 250fps and up with a well placed shot.

[Forum Admin]

That's where things start getting a bit difficult to answer.  A 1/2" marble has a horrible ballistic coefficient, which makes it shed its velocity very quickly. On top of that, the marble doesnt have much penetration at those speeds. It's kinda like getting hit with a fastball. A 90 mph pitch carries a whopping 85 fpe, enough to leave a bruise, but not normally lethal. A .22 bullet shot from 75 or so yards away will have similar energy and definitely penetrate into the body and have a good chance of being lethal.
Since you are limited in both velocity and energy, you might want to look into other types of ammo that offer better penetration. Small homemade arrows or darts are probably going to be your best bet for taking down groundhog sized game with less that 6 fpe. You'll want a broad cutting surface to open up as large a wound channel as possible so the animal will bleed out quickly. I'm thinking along the lines of a 1/8" cold steel rod with a 1/2" broadhead made of 12 gauge steel. If you use a 1/2" type L copper barrel, you can use a foam earplug as a stabilizer. Here's a page that shows a dart similar, just without the broadhead: http://www.airgununiverse.net/darts.html.

[chucker]

The fastball is a great explanation. I'm horrible at making darts and I just like the simplicity of ball ammo. I'v killed groundhogs with a 4ftlb .177 pellet gun before and crows with a slingshot and marbles, at 11ftlbs I figured a good headshot might take one down even without penetration.

[Forum Admin]

I like ball ammo myself, just patch and fire. Now a 11 fpe headshot just might deliver the knockout punch needed to put a groundhog down. I guess it will all boil down to shot placement.
If you havent tried making a nail dart yet, you might have better luck than previous dart making ventures. 3/4" schedule 80 pvc pipe makes a good barrel that fits a 12 gauge shotgun wad. I simply heat the head of the nail until it starts to turn color (not glowing, just a color change), push it into the wad. I twirl the nail to help me center the wad. Once they are spinning on the same axis, I cool the nail-wad junction with a bit of water and you have a very straight dart. Now all I pretty much shoot are nail darts and my good old trusty .58 cal lead ball. 

[chucker]

I tried to make some nail darts with the full sheet paper cones but, the cone just folds up and breaks whenever they hit something hard like 1/2 inch plywood . I may just give them another chance using foam discs or wads. I've decided to leave the airgun as a long barreled "pistol" since i cant find the right coupler and it looks wicked . accuracy is also good- 5 shot 1 inch group at 20 feet with 14 inch 3/4 pvc barrel and patched marble. Trying to hide the pilot hose in the grip is hard lol. I got some pictures of a water filled can I shot at 20 feet. It sprayed water over my entire garage including ceiling and tore the can a bit, so i think it has a tiny bit of shock even with the low power it has. gun is not finished thats why it looks like junk               -can entrance hole/rip
      -exit hole -i apoligize for the horrible quality images

[Forum Admin]

Glad I rechecked this post and found the pictures you posted. That's a pretty nice looking sprinkler valve airgun, especially considering it isnt finished. Pretty good power and accuracy as well. You just might be able to put a groundhog down with that.

[chucker]

If i can route the pilot hose in the grip along the chamber and valve i'll be happy with it. The grip needs a little more shaping and carving so you would just see the trigger of the blowgun sticking out, with no big hose trigger guard. I'm going to buy a 1/4 schrader valve off e-bay so it will look a cleaner, right now a bike schrader is held into a piece of hose with clamps. I wish i had the ability to make my own sprinkler type piston valve. You could make a nice all-metal compact valve, with a conical piston in place of the diaphragm. Any machinists on the forum? With the design i'm thinking of I think it would be strong enough for 500-1000psi. Problems would be finding a high pressure blowgun/making a push button valve, cushioning the piston so it doesn't hammer the valve apart, and finding a backstop.

[mouz]

my plan is to take the brass inside of a schrader valve and braze it into a copper or steel cap. it could not really leak. of course you could still over pressure the schrader, but i can only go to 400 psi so i don't think that will happen.