As one person replied - remember that a cannon can have quite a range when firing a projectile - whether it be a juice can filled with cement, a golf ball or something bigger. I used to shoot full size Civil War artillery - live fire - the group I was with had a full size 10 pound Parrott Rifle - we had one that was rifled and one that was smooth bore - we're talking a 3 inch projectile. At one event, we hit a junked out National Guard pickup at 1 1/4 miles - pretty much the maximum range of the 10 pound Parrott with a service load of 1 lb of powder. As with any firearm - USE IT SAFELY. I shudder when I think about what I have seen with how some gun crews operate. Yes, they are fun and they make a big bang - but, all it takes is a slight ember and someone not using a thumbstall on the vent while loading to have aa premature discharge - and folks, there were a LOT of one armed Civil War vets. as a result of this when the gun discharged while loading, thus sending the rammer out the barrel and into flight along with the #1 man's hand and arm. That is one reason why the thumb is NEVER wrapped around the rammer (it is kept straight and parallel with the rammer staff) when sponging, ramming or worming. While basically the muzzleloading cannon loads like a muzzleloading rifle, the vent MUST be thumbstalled (covered tightly) to prevent air from entering the bore from the vent when it is sponged and providing the possibility of an ember that is missed by the sponge. Normally, the powder charge is introduced first (we put our powder charge in a baggie and then wrapped it in a tin foil cylinder that was formed around a form that was just under the bore diameter size. Second, the projectile (if you are using one) is introduced and rammed. Even if the powder charge is contained in tin foil, accidents can happen and if the vent isn't thumbed, as the charge is put in and rammed, air is pushed down the barrel and up through the vent which can cause an ember to "glow and gain heat" - this could be from fouling, etc. - and thus ignite the charge early. To relate it to firearms, if anyone has ever seen a "cook-off" at an NSSA event when the muskets are being loaded fast and often during a timed event, you'll know what I mean - it ain't pretty. I really don't mean to "rant" - just realize that muzzleloading cannons are a creature all of their own and use safe practices, hearing and eye protection always. They can be a lot of fun - good luck with your project if you decide to put one together.