This device is very easy to build, quite safe (if you keep your distance) and marvelously noisy. It is simply an electronically fired mortar of surprising power, and can be modified in terms of power and manufacture to suit your specific environmental requirements.
Drill two small holes in the bottom of the film canister about half an inch apart. You don't necessarily need an electric drill to do this, but it makes the process appear more technical. You can wear a white lab coat too, to complete the mood. Break open the Polaroid flash bar and extract all ten bulbs, being careful to leave as much wire as possible extending from each bulb. Put one of the bulbs into the canister and insert the wires through the drilled holes. Put a small strip of tape over the holes to seal them and hold the bulb in place, leaving a bit of the wires exposed. Fill the canister with black powder (or half-fill, depending on how game you are. Try one of each for starters.) and place the cap on top. I usually connect about six inches of insulated wire to each of the protruding bulb wires to make it more manageable to handle, because the next step is to wrap the entire device (Hey... a device! It's starting to sound like the Manhattan project!) in duct tape. Use your own judgement on this, but ten or so thicknesses is about enough to contain the blast pressure effectively. Anyway, you're now the proud owner of a mortar charge.
Dig a shallow hole in the ground and place the lump' o'wood at the bottom. This acts as the baseplate for the mortar. Connect the 40ft insulated wire to the wires protruding from the bottom of the charge. (Make sure the other end of the wire is nowhere near electrical instruments, such as your cat playing with a styrofoam cup on a nylon carpet.) Put the charge on the wood and place the PVC tube over it and fill in the earth around it. You can rest the tube against something at roughly an 80 degree angle. Height of the projectile rather than distance is more impressive. Wrap some duct tape around the base of the soft drink can so it fits not-quite-snugly in the tube, i.e. slides down just like a real mortar projectile. Half fill the soft drink can with water (for momentum) and drop it in the end of the tube.
Stand back and connect the wires to the battery terminals. I think you can guess the rest. I've had one reach roughly 300ft. Very, very, cool. The reason I use such a loose base on the mortar is that the earth tends to absorb extraneous blast and no damage occurs to the PVC tube (surprisingly). You could make one with a sealed end, but this would have to be of all-metal construction hence costly, heavy, and potentially (more) dangerous.
Anyway, have lots of fun with this. It's not expensive, you can make heaps of charges if you get a production line going with a few friends, and it is actually quite safe if you avoid the explosive projectile idea (unlike a certain individual who shall remain nameless). I eventually did get one to blow in mid-air. That was VERY impressive.