Not something you'd do most days.... But you might do so IF you feel like playing around a bit! 1st thing is it MUST be a NON BREECH LOADING type. That is a real no no! I and a Boeing engineer played with making just a breech one week, where we designed the breech almost as they were in the recoiless rifles ( 75mm and larger...and someone called those rifles? Sheesh!) Anyway, we used the same breech design and we had it set up so you could use blank loaded 12 gauge rounds. Now making a metal device is NOT illegal, as long as there is no barrel for it to fit to! Any cartridge loading weapon (even though it may be only a party favor to some of us) must be cleared through the BATFE, ESPECIALLY IF it is above .50 caliber. It gets confusing when you really think about that.ANY caliber over .50? Really? Where did they get that from? Since most shotguns except .410, exceed that measurement by quite a bit! What about black powder in .54 caliber? Sheesh! Anyway....As I came to understand the "LAW"....you can make a lot of things, including weapons, IF they are NOT sold, but remain in your posession. Ok, I give up now! But we made this beautifully crafted design that would easily allow for a 12 gauge shell to be loaded into a"barrel" (if we'd had one) and the opening would only allow that size to be used, as the barrel would open up considerably to around 3 or maybe even 4 inches! Now that would have made a sweet cannon! You could launch a lot of things from that baby! We made 4 different types and designs of firing pins, where you could pull and release, or have a lanyard release, a lever-lock type of release and a type that you simply hit with a small hammer! The breech was formidable and weighed about 18-20 lbs when it was all said and done. The breech "block" was machined from solid aluminum,and the rest of the springs and firing pins, hardware, etc., were all made of stainless steel. We called the BATFE ( was ATF) and were told simply: NO you can't! Well that is UNLESS, you have a destructive device license! We did however discover that we could make black powder weapons and even cannons ( as long as the cannons did NOT fire a projectile) all day long! If we wanted to make a firing unit in a cannon size, then we had to have the very expensive license. We opted out. The breech plug was disassembled and destroyed...much to our chagrin. Seems black powder guns ( rifles anyway for the time being) is exempt from the law as it is a "Muzzleloaded" device. No so for those old Damascus and twist steel barreled BP shotguns. They were exempted too ( can't reason this out!), as well as those BP revolvers that use percussion caps. Too complicated or me to research! I was aksed repeatedky when we asked about a black powder cannon, if it were legal or not....IF it used a "wick"...?No it'sNOT a candle it's a black powder cannon! Well, according to those wonderous souls we all know and love, that work in the BATFE offices, a "wick" is a pyrotechnic device. Huh? If you say so! Funny, but I have been using "fuse" for many many years and I beg to "differ" the point, but the company that makes "safety fuse" is known to me as: "Ensign and Bickford" and they call their productcall it fuse, not WICK! Same same in the US Army! Go figure. So I was told in NO uncertain terms that ANY use of fuse is strictly prohibited unless you have the DD license in your posession. According to the BATFE people, the term "fuse" represents a mechanical device, used ONLY to set off an explosive charge! Maybe they watched too many movies on the History and Military channels? Yes, they are corect in that those are also called "fuses", that are used in munitions all over the world for all kinds of things. It gets stooopid is what it gets! But, be that as it may be...... You can build a cannon that uses Black powders, or Pyrodex propellants for your toy's! You can do that, as long as you understand it cannot in any way shape or form, shoot any type of projectile. It can use wadding. Now as for firng them ( Oh No!)...Here we go again...You cannot shoot one inside the city limits, UNLESS you have the written permission of NOT only the Police department's Chief or Commissioner, but also that of the Fire department.Now IF I choose to I can take my new toy out to one of the local lakes, BUT I have to get permission form the Sheriff's office and then I must also notify the Deputies at that lake, prior to any use or ignition of said device! So, I fired mine in a mobile home park! (With management's permission of course!) I promised, "NO earth shattering KABOOM"! No big bang, but a rather strange sound much like a dinosaur burping ( or passing gas?) It was a bit weird I'll admit, as it had a very small charge and only that, not even any sort of wadding at all....The flame was pretty and the smoke rings it produced were really awesome! I figured it was due to the length of the barrel/pipe, and the low amount of black powder I'd used. It was hilarousyl funny and everyone got a big kick out of the show! With the extra long barrel ( 4 1/2 feet) it was more of a weird sounding Shaolin device, that made a very LOOONG winded "BOOOOOONNNGGG"! Almost like a guy hitting a very long piece of pipe with a heavy rubber mallet! What an echo! You can make some interesting things like that, also those wonderfully LOUD little tubes that are used for signalling around ships! Man are those things LOUD! (PS) we NEVER got a response or any sort of answer or clarification to OUR question to the BATFE, "what if"....The cannon had a breech loading system, but could ONLY be used with black powder blanks such as are sold commercially? That was years back. I am not expecting an answer any time soon.... (So I guess they mean NO when they say NO to a breech loading cannon!) Dang it!