oh, and of course now the question becomes, how do I make this thing better?? We are getting about 50m from it now, what is it going to take to get more from this puppy?

It's a 3"-2", but yeah, it has held up nicely thus far. I don't think we've ever gone above 75psi more than once...we just weren't seeing an appreciable gain in range or velocity for the amount of gas that required...

Ok, here's my attempt at photos, these are all from the build, I will post photos of the final product when I get a chance a few days from now:

The tube; note the tube sticking out of the side, which I made the bottom, so the blowgun valve and handle would attach there...
http://i214.photobucket ...

Well, I have been very busy with work, so an update was not possible. I have photos of the construction and can shortly take photos of the final product. How do I post pics?!

The t-shirt cannon has been a hit at the football games, and we have been able to reach out to about 50 meters with it. We ...

Thanks for the info folks; I am getting there. I need to assemble everything in the tube, then mark the locations of my centering rings so I can drill holes for some screws to hold everything in place. And then the paint has to dry...

The two forward rings on the barrel are epoxied in place, while ...

Ok, so I ended up with an 18" chamber and 15" barrel, basically as discussed. I did not glue the sprinkler valve in, in case there was a failure of some kind.

Well, I couldn't resist testing it, even if the glue was not fully cured. I took it up to 60psi, and everything worked as I hoped; the shirt ...

BTW, we have plenty of ROTC stickers, we'll likely be adding those to the tube....

@veginator
Sorry, nothing to it but being 6" id and 48" oal....either aluminum or a very nice fiberglass job, it has such an odd tone when struck I honestly can't tell.

@DYI
Nope, I put down 5psi as a wild ass guess. And sadly, I am too far along now wih my 1" valve to change it; that and it was ...

Thanks again for the replies.

@Pete Zaria
I elected not to go coaxial upon further examination; the TOW tube does have a couple holes in it, I guess where the firing system interfaced with the mount or something. Also, I am short on time and did not want the hassle of getting 6" PVC for a chamber ...

Oh, another question; the nitrogen tank I have comes with a fill-tube and quick-detach female end for a 1/8 fill stem--wouldn't this preclude the need for a regulator? Is there a reason I can't just read a pressure gauge on my chamber and turn off the flow when satisfied? I can't imagine how the gas ...

Thanks all for the replies; I'm definitely aware of the uncertainty in getting the tube completely sealed, but my insistence on a 3" barrel stems from the need to fit the t-shirts.

Since sealing the tube would be so difficult, suppose I put a large piece of PVC into the launcher tube to act as a ...

Wow, for a forum dedicated to making potentially hazardous projectile weapons, some of you sure sound afraid of making something resembling an actual weapon...

To answer your questions, the t-shirts are to promote Army ROTC on my campus, so no one will be shocked to see a missile tube pointed at ...

All,
I have a spent TOW missile tube, which I plan to use to launch t-shirts. Trouble is, I have no idea what I am doing.

I would like to put a 3" barrel inside the tube, to make it look like a plain missile launcher when shooting the shirts. What is the proper term for this tube-within-a-tube ...