SpudFiles

I'm looking to build a cannon to fire Nerf Pocket Vortex footballs. The targets will be people, so obviously it has to be reasonably weak. Furthermore, I will pump it by hand, so the pressure has to be within the range of a floor pump.

From this, I need a 2" Sch. 40 PVC barrel. (All subsequent diameters are nominal.) The rest largely depends on the valve. I've seen piston valves strongly recommended for barrels of this size, and I'm not afraid to machine one if necessary. If possible, I'd like to use a coaxial configuration, and I don't want to go longer than about four feet. Given these parameters, I started playing around with GGDT.

Right now, I have it set at a 2" x 48" barrel with a 3" x 40" chamber (118.5 ci). I let it estimate the fiddly values for the valve, based on a barrel-sealing piston valve. At 60 psi, this supposedly results in a muzzle velocity of 334 ft/s (max range ~300 ft). Surprisingly (to me), 30 psi results in a muzzle velocity of 237 ft/s (max range 250 ft).

For reference, the projectiles (based on figures from this site) are 1.98" OD and 26 g.

So I have the following questions:

- Are the GGDT figures reasonable for such low pressure? I recall that GGDT is not really meant for pressures below that.

- Is 334 or 237 ft/s "people-friendly", even given the soft projectile?

- Would a QEV be practical for this? If so, would one of the <$20 QEVs that I see for paintball/airsoft work?

- Would a blowgun suffice as a pilot valve for the piston?

- Is there anything else that I should be considering but am not? It is my first fully homemade cannon.

Thanks in advance for any feedback.

I wouldn't recommend a piston valve for two reasons:

1) Way overkill

2) Quite difficult to seal a 2" piston with a floor pump


At what distance do you plan on shooting people? A 3/4" QEV or 1" sprinkler valve will be fine, 334fps is too quick for people.

Imagine a 30gram paintball hitting you at 330fps.

A blowgun could pilot a 2" piston, but you'd be wasting a lot of power.

I would use a 1/2" QEV with that 2" barrel, solely to limit the power.

I'll be firing from anywhere from 30 to 200 feet; below 50 I would just as soon pull out a Nerf sidearm.

Imagine a 30gram paintball hitting you at 330fps.

In all fairness, a soft foam rocket would probably sting less, but I see your point.

Is a 3/4" or 1/2" QEV the size used to upgrade paintball markers? If not, where would I look for one? McMaster seems to start at $100.

EDIT: Missed frankrede's post the first time.

EDIT 2: To be clear, this is for Nerf warring. The participants are known to tolerate hot glue-tipped lead-weighted darts firing over 200 feet, but would not take kindly to bruises.

If you really want to make it a pocket one... make a burst disk cartridge with a co2 inflator... the whole gun would fit in your pocket.

Thom wrote:I'll be firing from anywhere from 30 to 200 feet; below 50 I would just as soon pull out a Nerf sidearm.

Imagine a 30gram paintball hitting you at 330fps.

In all fairness, a soft foam rocket would probably sting less, but I see your point.

Is a 3/4" or 1/2" QEV the size used to upgrade paintball markers? If not, where would I look for one? McMaster seems to start at $100.

EDIT: Missed frankrede's post the first time.

EDIT 2: To be clear, this is for Nerf warring. The participants are known to tolerate hot glue-tipped lead-weighted darts firing over 200 feet, but would not take kindly to bruises.

All of mcmasters QEV are 20$ and under

I searched again, and I found the ones you're talking about; thanks.

Nerf Rockets have some umpf at 50 feet traveling 250 fps from the barrel.

If you plan to shoot at people i would stay under 175.

And this is from soemone who only shoots nerf rockets.

For in a war, you cant spend too much time pumping, so keep the pressure low, but build your gun to hold higher.
Also, a longer distance calls for more pressure and speed, since it will be slowed down when it got there anyway.

To limit the power, keep the pressure low and the resevoir small to avoid long pump-times.

Hey, by any chance, are you from nerfhaven?

Damn, why doesnt someone build a nerf law, powered by CO2 and work out how much pressure they need for distances, add a rangefinder and voila, problem sorted.

Technically all they need is the rangefinder, but you could just go with dead reckoning.

Because that's completely unnecessary and the fittings are hard to find for most nerf gunners. They don't usually have access to alot of the resources we do. A notable exception would be one called Boltsniper, who has built a number of very well made systems that rival our best pneumatics for ingenuity. One of his creations is a semi auto gravity magazine fed gun from a 12gram CO2 cartridge.


EDIT: Engrish.

In light of socoj's recommendation, I'll definitely scale this thing down. Before I figure the final numbers, though, I have two more questions. First, would a change of form factor be advisable to avoid bending the airflow? Second, how does one input "QEV" into GGDT? Is it "Generic"? What are reasonable settings?

Hey, by any chance, are you from nerfhaven?

Yep. Same username.

Ah. Guessed so. Nerf guns aren't exactly common around here. But I bet if you looked around a bit you could make something that makes a singled Titan look wimpy.

After yet more searching, I still can't figure out how to tell GGDT that I'm using a QEV. I'm sure I'm not the first person to ever try this. Would someone throw me a bone here?