The Messenger

[julz]

i recently built my own cannon. it has a 2.5:1 air chamber to barrel ratio and the barrel is 1metre long by 1inch.
at sixty psi it shot a cork coated in tissue with a lead fishing sinker at the front for weight. this is all wrapped up in duct tape. it got through the pump box, three magazines and hit the brick wall behind it, completely squashing the sinker.
i'll try to get pics but don't have a camera so they'll prob. take a while

EDIT: I GOT PICS!!!!!!!!!!

these are after the bigger chamber mod

if the image doesn't work try

[iamthewalrus]

what kinda sprinkler valve did u use, modded or electric??

[julz]

electric. i thought it was really hard but then realised it is just simple so did that. i have now got a new pump and at 100 psi it shot a spud 100m up in the air. then i made a target out of thick cardboard, folded it to 4x and shot straight through with the above ammo. then i made datrs out of old dart tails, cork, padding and bolts for weight. tyhey shoot far further than spuds and at 60psi they went anout 70 metres before hitting a tree down the road. also i added a silencer that is great. now the sound is just a muffled bang instead of the huge crack i got b4. good for residential areas . now im looking to make a rocket or something else that flies a f.u.c.k load further than spuds. also i have yet to try my C batteries.

next additions: laser sight
rockets
bigger chamber (maybe)
clone with a mate and combustion with bro.

ps. if i make the chamber bigger but still pump it up to 100psi will it shoot further? i guess my question is--> is it only the pressure that matters, or also the volume of air.

--Julz

[drac]

It's the volume of air. 50psi in a 100 ci chamber will outperform 100 psi in a 14ci chamber.

Edit: Didn't notice the 100 m vertical. Another Luckythirteen quote:

F*CK!NG $H!T!!!!

That's impressive to be able to have a spud going at 90* vertical for an entire soccer/football field. I can barely get mine to go that far at a 45* angle.

[julz]

ok thanks Drac. i reckon i'll get some couplers and add some more volume in my chamber.

[iamthewalrus]

tank size really matters, i had a pistol, when i pumped it to 180psi i couldnt even go through a hubcap with a battery(not on a car) with its liike 2in tank. now with my new paintball sniper with a much larger tank i can go through a hub cap with a paintball at only 80psi. and my sniper can clear 100yrds at about a 10*. my pistol only went about 50yrds at 45*

[julz]

sweet. i will mod my chamber as soon as i can. probly on the weekend. also i will tell you all of my new ammo. i made a rocket out of a bike pump and put a plastic dart tail on the end, then PVC glued it to 'weld' ity together. this thing is gonna FLY! i just hope i don't hit a tree cos it'll shatter and i will have to make another
---Julz

[iamthewalrus]

ur gun would shoot even farther still if u modded ur sprinkler valve. modded ones oven like 2x fater then electric ones. and no more batteries.

[PhoenixFire]

Another thing that matters is barrel length, A longer barrel gives the potato more time to accelerate faster, but the length you need for a cetain speed increases exponentially due to wind resistance in the barrel. Another thing to consider is the width of the barrel. wider is generally better if the projectiles weigh the same. the area of the cross section needed will also increase exponentially. Keep in mind that the exponentiall part really only matters if you're attempting to get some seriously wicked speed.

Furthermore the barrel to tank ratio determines the pressure drop in the barrel. For example with a 1:1 ratio, charged to 100 psi, pressure at the beginning of the shot will be 100 psi, and at the end will be 50 leaving an average of 75 psi of pressure. now take a 1:2 ratio. Now at the beginning the pressure will be 100psi and at the end 66.6 psi. this gives an average of 83.3 psi. Now a 1:3 ratio gives 100 psi and 75 psi with an average force of ~81 psi. Any ration above 1:4 is virtually useless as the gains keep decreasing as you move up.

Also woth considering is the turbulence in the gun. The more angles you use the more turbulence you get, the air flows with less power. Sprinkler valve have the most turbulence, custom diaphragm's pistons, etc have less, and ball valves have the least, except you can't turn a ball valve nearly fast enough to get good performance without some serious pulleys and springs. in generqal you want as few twists and turns as you can.

[julz]

PhoenixFire; Wow thats a lot to know about spud guns
anyway, thanks for that info. can you answer some questions?
i haze a two 90* bends and the chamber varies in size from 2" to 1.5", then it hits a sprinkler valve and a 1" barrel. will this effect the airflow much? ie. turbulence?
if you have time can you please explain the seond paragraph a bit more? i dont really understand(i think i do but im not sure)

iamthewalrus: try shooting at 30-35*, due to drag and different air presssures 45* is not the ideal elevation, 30-35 is. i got that from some site bout projectiles. said that 45 is best for a vacuum.

as for my sprinkler valve, could it open faster if i widened the factory holes that the solenoid opens and closes? this would be like a blowgun thing only just a little bit smaller. i promise i will get pics soon and have an update on my improvements
---Julz

Edit; forgot ot tell u. i made the chamber 12" longer at with 2" pvc and added a golf ball barrel. yet to try them out! then i will test my homemade darts and rocket, all with stabilising fins at the rear and weighting at the front.
---Julz

[PhoenixFire]

The two 90 deg. bends should be fine. What I mean to look out for are those guns like the sniper with a lot of twists and elbows. It looks really nice, but sacrifices some in power. It's all up to what you want out of you're gun. As for the paragraph on chamber to barrel ratios this should help. It's a graph of what the power output would look like according to the chamber size.

Plx ignorethe x's
|xxxxxxxxxxxxxxxxxxxxxxxxxxx
| xxxxxxxxxxx___.........---------
| xxxx_---"""""
|xx_-
|xx-
|x/
|x|_________________________

All it means is that as the higher you're barrel to chamber ratio, the less gain you're going to get out of each increase.


And I don't think the trouble of modding the hole for the solenoid would be worth the gain. i'm kind of worried that a larger hole would make extra pressure and causem the little spring that holds the solenoid down to give and prematurely fire the valve. It might even be easier to just do the blowgun mod. Personally since i have a compressor and can fill the tank b4 my finger tires i don't even use a blowgun, I hold my finger over the end of a vinyl Itube.

[julz]

sweet, thanks man. i get it now.
---Julz

EDIT: the cannon broke a while back after i did the chamber enlargement, but now i think its fixed! i just put it back to the origonal size and hope to test it tomerrow morning! wish me luck!

(this is my first post in a long while, so hi!)

from spudshot: you should know not to double post


^^^@spudshot: wot do u maen? i didnt did i?