Hey spudfiles!

[Dairyfarmer]

So I've been lurking these forums since about 2006 and I always wanted to build my own cannon. Eventually in 2008 I just sortof did it one day, after years of thoughts and drawings, and this is what I came up with.
It's a coaxial, both the barrel and the chamber are 10 feet long, because where I'm from, pipe comes in 10 foot lengths, and i thought it a waste to cut the pipe and throw some away. More gun for the same fittings was my motto. I felt like I owed it to the community to show them what I'd done (also want a bit of respect for making a giant coaxial)
Pretty standard stuff. Coaxial pison valve made out of a 3" endcap, tire innertube sealing face, 3/4" ballvalve for porting. chamber is 10' of 4", barrel is same length 1.5" supported in the middle with blocks of wood glued on. After a year the blocks came off when i fired it because they restricted the airflow, so i glued them to a cardboard tube, and slid it in, works great.

Let me know what you think! :)

[jackssmirkingrevenge]

Looks good! I do however have a complaint.

Even at low pressures, an exhaust valve cannon that big is bound to be capable of considerable muzzle energy, where are there damage picures/videos

[Dairyfarmer]

The only videos I currently have are on facebook

http://www.facebook.com/video/video.php?v=215005700620

http://www.facebook.com/video/video.php?v=215001305620

Sorry i have no more damage videos but I ran out of stuff to shoot at very quickly, and took far too few pictures because I was having too much fun shooting, I'm sure everyone understands. The most satisfying moment actually wasn't blowing stuff up though, it was that first potato that I decided to shoot up, instead of across, and it disappeared through the clouds. Made me so proud.

[jackssmirkingrevenge]

hehe, you'll soon find yourself setting stuff aside to shoot at instead of throwing it away

The muzzle report is a little odd, sounds like you might be having a little piston bounce, can the piston travel far? You might want to consider a sprinkler valve pilot, it will make it easier to fire and more consistent.

[Dairyfarmer]

The sound is because i leave the fill hose on, and it whistles. If I shut the fill off it makes a nice crack sound, followed immediately by what i can best describe as a whumpah sound, as the projectile exits the barrel. The only things I'd do differently on this would be a) breech loading (seriously 10' ramrod is a PITA. b) longer barrel, much longer. I cant remember what my C:B ratio is anymore but Its pretty horrendously large.

In other news I have a new idea for a coaxial breech loader using a hole cut into the side of the barrel, and the barrel would be longer than the chamber, and stick out both ends. you place the projectile in the cutaway in the barrel, and then slide the barrel into the chamber(whole barrel slides) as soon as it is inside, the air goes in that same hole and it fires. Has this been done before?

[pneumaticcannons]

I cant remember what my C:B ratio is anymore but Its pretty horrendously large.

You're complaining?
Nice job, as jack suggested, try Piloting it with a sprinkler valve. Before I posted the cannon I linked above, I was using the same type of PVC ball valve as the pilot. Switched to a sprinkler valve and not only saw an increase in performance put also in accuracy.

[cammyd32]

Dang! that is a big cannon! nice job with that
only improvements I can suggest apart from the ones aforementioned is to possibly make a custom stand/trailer for it and a give it a snazzy paintjob really impressive cannon, congrats