SpudFiles

Okay, I'm designing a LAW for paintball that shoots min Nerf vortex footballs (thay are 2" in diameter).

Here's my design so far...




I want it to shoot around 230 fps. I plan on making the air chamber out of 2" diameter Schedule 40 PVC. I want the gun to operate around 30-60 psi.

How long should I make the air chamber for this too work?

Use pressure rated pvc fittings (sch-40), not dwv or abs fittings.

I know. I made sure of the fittings.

So got an answer to my main question?

not sure how to figure the math on that to get the fps, There are to many variables; weight of the ammo, resistance going down the barrel etc. I would make it the way you have it drawn and expirement with different air pressure to get the distance you want, 30 psi to 60 psi seems pretty mild. Why ae using sch80 rather than 40? Sch 40 has an inner diameter a tiny bit over 2" on average and shd 80 is under 2 inches a little. I think I would go with a 3" chamber the same length as your barrel and start with a low pressure and work up until I got the distance. The look of the gun would match what you are trying to do.

I see now that the diagram says sch 80 but your post says sch 40.

2 ft long. If you are going to carry this around make it small and compact.

I am making the chamber out of Schedule 40.

I can't do 3" diameter with the valve I have chosen, and I don't want to switch valves.

you can use a 3" chamber with the valve. All you need is a 3" to 1" bushing. Besides, you don't want to use reducers anyway. They don't hold as much pressure.

I have had bad experience with those valves.
Their shape make it prone to snap your threads going into your valve. It has happened twice and 26$ for the valve I bought I stopped buying them after it snapped twice.

"Use pressure rated pvc fittings (sch-40), not dwv or abs fittings." ~Benstern

Benstern, while your at it why don't you tell him to wipe his ass after he takes a sh*t? Talk about the basics...

As others have stated, it appears that possibly you intended to use bell reducers. Instead use a reducing bushing, as these allow longer socket depths on connections. I must note that for this issue in particular with bell reducer versus, bushing, wall thickness is not the issue, rather the shorter socket depths. Just thought Id point out as that is often times confused.

Just because everyone else seems to be taking the day off in the answering of your question, I decided to be so nice as to enter the data into GGDT! [If you are not aware of such software, Google the name "GGDT"]

Well I entered the given data into the program, the continued to screen shot the results. Listed are the two variation I tryed.
<a href="http://www.spudfiles.com/uploader/uploa ... mental.GIF ">3' Chamber/ Barrel @ 60PSI</a>
<a href="http://www.spudfiles.com/uploader/uploa ... ental1.GIF ">2' Chamber/ Barrel @ 60PSI</a>

Note: I very well could have botched any chance of accurate results with my horrible guesstimation on the projectile info.

The whole reducer deal. Well it doesn't matter which size your valve is, you could in theory go from 24" to the 1" threads for your valve. Although such would require more then one step. Also the step in availablity and price between 2", and 3" is rather noticeable. No worry though, 2" will suit the application just well.

As to the valve you intend to use, I have no prior experience with them. FrankRede seems to not had such a good experience with them, but I'm not sure it was out of the abuse of simply securing the chamber and barrel together, or something of that nature. I don't know how the threads by them selfs could just cause the male threads to 'snap'.

The threads snapped because he evidently had no barrel support. Eventually, the weight from the barrel would stress out the threads and make them break off.
Elemental, you can use that valve easily, just make sure you have a sturdy barrel support near the end of your barrel and chamber.
Other than that, it looks like a cool design. I'd love to see that with a flat brown and olive paint job.

Pimpmann, wouldn't the 3" chamber give a higher muzzle velocity than the 2" chamber if they were the same lengths and the same pressure?


I've decided to return my original valve and am going to get a normal 1" inline valve. This way, I'll be able to use a 3" chamber.

But, what is the best way to reduce from a 3" chamber to 1" piece without bell reducers?


Also, I have a crazy idea for the paint job. I'm going to do Eddie Van Halen's "Frankenstein" paint job, but with olive drab, black, and brown.

P.S. That was just a design idea, I am using reducing bushings.

Use a 2" chamber, you won't have velocities able to hurt someone, and it'll be more compact. How does an inline valve let you use the 3" chamber?

"How does an inline valve let you use the 3" chamber?" ~Noname

Easy, a 3x2, and a 2x1 bushing.

"Use a 2" chamber, you won't have velocities able to hurt someone, and it'll be more compact." ~Noname

Well I'm not going to support the difference between a 2", and 3" chamber will result in injury, although I would support the claim that it would increase the chance. I also don't think a 2", to 3" chamber will effect how 'compact' the given launcher. Such a addition is going to add ~1" to the height, and ~2" to the width, while leaving the length the same. Length being the issue.

As Noname said, quite possibly in FrankRede's design the threads 'snapped' from the shear stand out weight created by both chamber and barrel. Fastening the chamber and barrel together would eliminate such stress. I suppose that there is a advantage to over-under designs, that one can fasten the two together and eliminate stand out stress put on small diameter joints.

The reason I did not suggest a 3" chamber is that the 2" x 2' version surpassed your request by a estimated 50 FPS, with the 2" x 3' version by ~90FPS. Personally I see no reason for the larger diameter chamber. As you suspected, yes I would believe while increasing the chamber volume that such would result in greater velocities.

I suggest if you'd like to return any result pertaining to the 3" chambered launcher that you download the GGDT software, and run the numbers yourself.

Yay for the Van Halen paintjob. Why not the traditional red with black and white stripes?

Bluetooth wrote:Yay for the Van Halen paintjob. Why not the traditional red with black and white stripes?

Cause I'm using it in the woods and I don't want to stick out like a sore thumb when I go tank hunting.

I think I will make it pneumatic. How does a 3" air chamber that's 3 feet long sound?


For it to be field legal, it needs to stay under 230 fps. Pimpmann, I know you said the 3" chamber will cause me to surpass this velocity by 90 fps, but remember, I'm using an adjustable regulator (a Palmer Stabilizer (best paintball reg IMO)) that can go from 0psi-800psi. So if it's shooting too fast, I'll just turn down the output pressure of the reg.