Okay, I went with a Max 1500psi pressure in mind, with a 2x safety factor of 3000psi working pressure. Very generous, because I doubt that I would go over 8x mix to begin with.

12 5/8" grd 5 steel bolts on each end works out to about 265K lbs of shear strength on each end, that should be plenty ...

I will go for the high-strength steel rods and bolts then. I like your idea of hydro testing first. Keep in mind I won't be anywhere near this thing when firing, remote ignition is mandatory.

assuming 1500psi max pressure...

that would put about 19,000 lbs of on each 4" section and 42,500 lbs ...

Thank you Moonbogg, I did not think of that. How about this instead:

http://postimage.org/image/epc3wypb5/

Nobody has posted about the barrel-lock mechanism so why not use it at the back as well? I would, of course, extend the chamber length to maintain the chamber volume.

The only downside I can ...

Hell ya, 6061 Al is cheap! I didn't realize that it would be as strong as steel so this will probably save me $500.

I promise to post pics when things start to come together more! Maybe if you're lucky there will be some test shot vids in maybe a month or 2. :) :o

Any last suggestions before I ...

Thanks for helping out a noob, you guys.

I will bevel the edge and extend the piston.

I just realized that going all-aluminum may be cheaper and easier than steel. 6" sch 40 Al is about 1/4 the price of sch 80 steel and could do 1000PSI easily, much lighter too. I imagine drilling 30-40 holes ...

Ok thanks guys :)

About the limited flow... I know that it looks restricted from the drawing, I thought so too, but the flow area is still over twice as much as the inner barrel area (4.3 in^2 and 2.0 in^2 respectively). If I beveled the Al block a 1/4" around it would be more then enough, I ...

Ok, here is a better piston, i hope?
:lol:

http://postimage.org/image/ovnoxur7h/

This design is roughly to-scale, each blue line is 1/4"

I added a flange to the breach to reduce piston area, and reduced the piston to 1" long. I'm also thinking of using high-impact plastic instead of Al.

The ...

Again, killer advice man!

I will redesign the piston and go with the 2/3 barrel to piston I think. That makes much more sense. I'll post a scan when I'm done with some numbers too, may take a bit though.

I looked at some of your cannons, very nice!

Mr. Crowley,

Thanks again for your detailed reply! "850PSI" Uh yeah... that sounds like it would be very dangerous to anything behind it! I would have to do some better designing for those kinds of forces. I was generous with the piston travel distance and diameter, but perhaps I will do a ...

Thanks for your input :-) Just a few questions if you don't mind...

About the pilot pressure: I see what you mean about having a higher pilot pressure. What would you suggest for for pilot pressure if the chamber pressure was 100psi? I suppose I wouldn't need the spring if I did it that way. Hmmmmm ...

Hi guys, just drew-up a design and would like to hear what you guys think. Constructive criticism, suggestions, and flaming are heavily encouraged!

This launcher is a hybrid type using a classic piston valve design and propane. I designed it to be constructed with relatively few parts with minimal ...