A bowling balls diameter averages 8.6", so if one were to use 10" x 0.500"wt; seamless X-60 pipe you will have a actual bore of 9.75". Weld a cap meeting the same specs on one end and call it good.
Off hand I don't know the yield on said pipe, but it should be sufficient for firing a bowling ball. At a weight of about 55 pounds per linear foot it would be pretty tough to tote around though.
I do agree that sewer pipe is a poor choice.
"I do agree that sewer pipe is a poor choice." I'm not a pipe guy, but would gas pipe, as in mains, be a better choice?
This looks like a fun project though I have a couple of improvements in mind.
First, an electronic ignition sytem, such as a model rocket ignitor system, would be far safer than a manual fuse.
Second, some sort of carriage type base, where the barrel sits on a slide and has springs similar to heavy duty trucks to absorb recoil. And, mount it all on a trailer with swing out down jack plates at the corners for stability.
The modeling portion of R and D starts tomorrow.
It's been too long for me to go and look up the right formulas for gas pressures but below is the basic information for determining chamber pressures for this pipe bomb. SAAMI doesn't seem to say too much about black powder antics since they are devoted to the issues surrounding modern smokeless propellents.
I did find some stuff about black powder artillery and have listed that below, too. Seems these fellows think this should be classified as a cannon on the basis of the ratio of the projectile length and the bore diameter. In any event, they specify a yield strength of 85,000 psi for safe barrels. That's a long, long way from 2,900 psi.
Mortar safety:
http://cthulhu.control.com/~emoore/AAA/mrt.html Cannon safety:
http://cthulhu.control.com/~emoore/marty.html General black powder information:
http://www.aeroballisticsonline.com/articles/blackpowder.html "Blackpowder is a comparatively inefficient powder. One gram of blackpowder gives you 718 calories of heat, 270 cubic centimeters of gas, and about half of a gram of residue."
Gas Volume generated by "3 ounces" of black powder:
3 ounces = (28 x 3) = ~84 grams
84 x 270 cc. = 22,680 cc. = (22,680/1,000) = 22.69 liters of gas volume
Chamber dimensions for an 8" diameter barrel with 3' length:
(3.1428) x (16) = 50.2848 square inches
(50.2848) x 36 = 1810.253 cubic inches = 29.67 liters
Volume of gas in excess of containment vessel volume:
(29.67) - (22.69) = 6.98 liters
The ballasticians and physicists out there should be able to make sense out of that information.
For those that value their eyes and limbs and would like to continue sucking air, here's a cool firm that specializes in the real thing:
http://www.cannonsonline.com/midas/co_r_showCat.asp?category=5