My bovine safe pneumatic

[notarobot]

Does GGDT send you secret messages about what guys are modeling?
Just kidding.

Your post is interesting because I made a new barrel last night of 5/8 bore pvc lining 3/4 copper 17" long. Then came in and started modeling changing the chamber size vs velocity gain %.
I settled on a 6" length of 1" rigid copper for the 100 psi chamber. Then I started bumping up the pressure and shortening the chamber to see what happens.
Since I am using type "M" copper, I can go to 300 psi if I lose the shark-bite muzzle cap. There is a local company which sells the low temp solder Stay-Brite which lets me theoretically go to 500 psi since it won't anneal the copper (if I am careful). Those numbers bump up about 100 psi for type "L".
The copper ratings are from a mfr"s web site.
I'm not worried about the pvc vs higher pressure here as the pvc fit in the copper is pretty tight.
If there are any worries I could also make the joints leaky (I use three pieces) and allow the pressure to equalize inside and outside the pvc liner.

Just as you all predicted, it's pretty obvious: I need more pressure!

[farcticox1]

Yeah, sometimes the parts dictate the layout.

BTW, love that chamber to barrel ratio.
What is that silver cylinder between the chamber and the QEV?

It's a 1/2" Npt nipple with 1/8" thread welded on the top and the end capped off. The flat pieces are to attach the grip.

[Spudinator]

If you ever need some tips on how to run your lathe I could probably help out a bit, I've run a few in my days (been a machinist for 12 years). And like jackssmirkingrevenge says, a smaller chamber and higher pressure will go a long ways, literally lol. Soldered copper tubing can hold a couple hundred PSI and it does not grenade like plastics can, and looks sexy to boot when polished up. Probably a damn sight cheaper than brass tubing and fittings as well.

That setup in your last post looks pretty slick, I like the Idea of using the Sharkbite fitting (though a little spendy heh). You might be able to get a little more velocity from a longer barrel though, that looks pretty stubby for the size of the ammo you are shooting.

You mentioned using a rubber washer pressed between two pipe ends to retain ammo, I like the idea but I'm not sure if it will last too long, how much of the washer will be clamped down? I guess it all depends on the pipe wall thickness... Maybe cut a slight internal taper on the ends of each tube to "Bite" the washer with your lathe?

Well anywho like I was saying I've got some experience with Machine equipment, If you need any advice on tooling or processes I can probably help you out. Ohh, you mentioned warping the tube on your lathe, if you cut a slug (or "Cookie" in machine lingo) of aluminum/wood with the same OD as the ID of your tube you can insert that into the tube end and get a much better grip with your chuck, without worrying about deforming the tube or having the tube attempt to chew holes in your face after flying out of the chuck heh.

[EDIT] missed your last post disregard the longer barrel statement, you were way ahead of me lol

[notarobot]

Spudinator said:

Thanks for the thoughtful comments and offer to assist.
There is no question that I know very little about the right way to operate the lathe. A machinist would probably have a heart attack if he watched me one day. A couple of knowledgeable friends have guided me in several areas, especially safety. The basic concepts of a lathe and machining seem rather straightforward. The application of same never quite turns out as well as I planned. But I persevere.
I did try your "cookie" suggestion. It worked (as anyone with an ounce of brains would have agreed), when I needed to ream the pieces of pvc a little more to allow a greater percentage of the gum balls to pass through the barrel. If only pipe was a bit more consistent dimensionally.
The shark bite fittings were removed from service after a maybe a decade. They showed minor signs of leakage, but were in otherwise in good shape. Rated at 200 psi, I figured "why not?".
Agreed, rigid copper appears to be the best bet in the future. The gum balls called for standard 1/2" pipe in brass. This is one case of find cheap ammo, locate a barrel that fits.
Regarding the washer, I made it as easy as possible for the ball to pass through the center by removing material so there were only three points where the washer material had to flex. Even though, the first was too thin and followed the ball downrange in excess of 200 fps. It's replacement is 5/32 rubber gasket material. We will see how this holds up. The newest short barrel has a steel spring "U" to retain the ball. It is still on probation.

I am looking really hard at more pressure. A local bike shop stocks shock pumps, and I was tempted to go there and talk to them. I need to read the Gippetto thread again and think on this.

[jackssmirkingrevenge]

If you're interested in a lathe project that will teach you the basics, this is fantastic with videos and plans for each step: http://www.spudfiles.com/miniature-cann ... 22856.html

At the end of it you get a sweet pneumatic pen gun!

[notarobot]

That is some really nice machine work there.
I read through your three projects re the penguns.
I'm afraid my patience places me a lot closer to the mixing epoxy method rather than machining parts.

I remember that you posted about self contained cartridges recently.
I was thinking that my next project could be a steampunkish revolver using fat penguns as cartridges.

[farcticox1]

He's going to use exploding penguins

[notarobot]

Ha.
You made me go back and check my spelling.

[Daltonultra]

That Grainger QEV is exactly the smae valve I use for my dart gun. I use a Cold Steel .625caliber blowgun for a barrel. It fits snugly over 1/2 copper pipe, so it all fits together nicely. Someday I'll get around to making a bolt for it. It fires the Cold Steel .625 mini-boradhead dart hard enough to penetrate completely through a 4X4 post, and it treats automotive sheetmetal like tissue paper.

[notarobot]

That is quite impressive.
What pressure are you using and which model Cold Steel blow gun? I will have to look into this some more.

One of the annoying things about using plumbing materials for parts is the crazy variation in the dimensions. Although the copper tubing is a lot better than pipe, I have a hand full of older copper 1/2" tees which are much too tight for tubing.