SpudFiles

I'm new, so if I'm being stupid and missed a thread similar to this elsewhere, just point me in the right direction and call me a noob. (I did look through a quick search and didn't find anything).

Skip down to: "QUESTION:" if you don't want to hear me babble.

I'm building a pneumatic gun for use with lacrosse balls that needs to hit 60-100mph, which will then hit a target approximately 2-3 feet away from the end of the barrel in a chamber. Yes, this is my job

As this is being used in a place of business (granted, in a warehouse), safety is a primary concern. Space constraints are also important.

I've played around with GGDT and came up with the following, all pipes pressure-rated PVC. Lacrosse balls are just under 2.5" diam and weigh ~140g (5oz).

Barrel: 2' x 2.5"
Orbit WaterMaster 1" Sprinkler Valve (or similar, modified for blowgun trigger).
2gal capacity tank with 1" fitting (PN #9888K11 at McMaster)
1" fittings from tank to
2 90 degree elbows to get an over/under setup, various connectors.

Now, the issue comes in that I also need a 3" diameter barrel for field hockey balls (diameter of approx 2.8-2.9in).

I also need relatively quick loading - due to space constraints, it will be hard to muzzle load.

so, for the TLDR crowd:

QUESTION: What's the best option for combine fast reload where muzzle loading would be difficult in addition to replaceable barrels in 2.5 & 3" diameters? Would rather not have to get TOO much custom machining done, but a little is acceptable.

bonus question: GGDT says my needed velocities are quite achievable, but is there a more robust valve I should be looking at instead of the iffy sprinkler valve mod?


Picture is of a similar setup, but far more advanced that I need to go (if I had infinite cheap labor and a bottomless parts budget mine would look a lot like this though!). Link goes to another similar setup, although I'd like to compact it a bit. http://www.soimpact.com/1Cannon.jpg

Biged uses exhaust pipe on his bazooka, (2.75" exhaust pipe has a 2.625id) along with a sliding breech cover for ease of loading.

You might have to have an bushing made (check stock od's) to weld on to the end of the pipe and convert it to 1"npt, but it should be an effective solution.

A second barrel for the 3" could be similarly fashioned, and simply threaded into place.

Any muffler shop should be able to help you out with the sliding breech piece if you decide to use exhaust pipe.

Biged's bazooka and mortar can be found in the pneumatic showcase section.

Thanks for the tip. I may use an aluminum pipe instead of PVC for the barrel if I can't find PVC that fits well (mcmaster has a lot of options, but the IDs vary a lot). Aluminum would also make machining of a breach loading system easier too. It would also probably be "safer", although I really doubt <100psi will shatter a barrel.

You may want to look into quick exhaust valves, as they can be bought from a number of stores, and they are usually made of metal, so you won't have to worry about the pressure too much. With a 1" sprinkler valve you may need to use a large chamber or high pressure to achieve the velocities you want, especially with a short-ish barrel.

For a barrel, you could sleeve two sections of 3" pvc to get a barrel that will shoot a lacrosse ball with just a little bit of wadding.

For a breech, you could make a ball valve breech, but that would probably get expensive with a 2.5"+ barrel diameter.

I may give up on breach loading and just go muzzle. Not as elegant, surely, but I'll need to retrieve the ball from the chamber after each shot anyway.

I ran GGDT with the supplied numbers for the 1" sprinkler valve (mod) to get my numbers and speeds - have you guys found this to be inaccurate? It does seem to be giving me pretty low PSI levels (<30psi for 60mph exit speed), but I figure even if it's pretty far off I have a lot of leeway on pressure.

Wadding is probably not an option, as my target is only going to be 2-3 feet from the exit of the barrel and I'll be taking high speed photography of the impact. The condition of the target and pressure distribution will be important, and I'm afraid a secondary impact from wadding could mess with the results some.

what kind of project is this? it sounds very interesting

-one easy breech-loading method is to cut a hole in the top of your barrel near the base, and then grind out a tee so that it slides over the barrel (o-rings optional) and the you simply rotate it up and drop the ball in, then rotate it down before you fire

Mostly for failure testing on protective eyewear, some protective padding stuff too (and possibly lacrosse head studies).

Pros can shoot at over 110mph... which is just scary. that's over 140j. The protective standard for Motorcycle crash equipment is only a 50j impact!


EDIT: Also having a real difficult time finding a good reducer for 2-1/2" to 1" (or at least 2" so I can use more standard connections) that's pressure rated. The best I can find besides 150psi rated iron bells (not too comfortable with that) is steel bushing+reducer combo... which will cost me about $100 per barrel. Ouch. Is there a good solution out there, or a website with a better selection of rated PVC fittings than McMaster?

sweet, if you still want a simple breech loding technique, mine is probably the easiest without sofisticated tools

Anybody try using flexible plastic tubing (pressure rated to 150psi) instead of PVC? I see it being much safer than PVC (if it explodes, it just ruptures because it's flexible, instead of shattering and sending shards everywhere), plus the smooth curves instead of elbows could help reduce pressure drop.

There's some pretty cheap braid reinforced EVA tubing rated for air @150psi at McMaster (5632K43 and various other sizes) with large inside diameters.

yes? no? A pain in the ass to find correct connectors to work with NPT threads?