in very basic terms (no way in hell I would take on the responsibility of giving you more detailed advice or God forbid a recipe, that you could mis-use and hurt yourself or someone else)-
to get a larger bang with lower danger-
1. use faster burning powder. the sharp bang (as opposed to the 'poof') isn't so much a matter of a bigger explosion (though obviously bigger explosions make a bigger noise), but a quicker one. use the smallest amount possible to get the desired effect.
2. contain the explosion for as long as possible with a very sudden release. the explosion is just the gasses from the powder burning being released quickly to take up as much area as you have gasses. the only real difference between a propellant type explosion and simply releasing gasses (like venting an air compressor) is the time available for the atmosphere around it to adjust to the presence of the new gasses.
what this means for you is to contain the explosion for as long as possible during the pressure build up until the containment fails. containments that fail slowly are more like a vent and give the 'poof', those that hold as long as possible and then have a complete and sudden failure give a very sharp bang.
the most important thing to always keep in mind is that whatever you use for this containment is going to ultimately end up as shrapnel. this rules out some otherwise great choices like a chunk of steel pipe for your containment.
I built a lot of fireworks when I was younger (up to the day of the attack on the OK-city federal building. it was fairly obvious that the rules had changed instantly and building your own fireworks at home was no longer going to be looked at as just a harmless hobby for the barely sane), my favorite was to wrap the powder in masking tape, then cover that with packing tape (the kind with the nylon strings running through it.
tape works much better than the standard paper wraps you find in firecrackers, each layer sticks to the one below and holds it together for longer, so you get a louder bang. the nylon tape is very strong but melts with heat. so I used the masking tape first (to slow down the heat getting to the nylon tape), then wrap it up tight with the nylon for a stronger containment that will hold back the explosion a bit better.
whatever you use you shouldn't have anything that would be hard enough to do damage, even a wad of paper is pretty damn hard if you get it moving fast enough, so don't use anything like metal, hard plastic, or glues that harden up solid like epoxy.
3. another thing for safety is to put your containment just over the actual charge instead of the whole piece (are you using some sort of smoke or chalk to mark the explosions or just going for the bang?). there are 2 very good reasons for this. first bigger containers hold less pressure so you won't get as big of a bang for your buck. the second is safety, a bigger container means bigger pieces sent flying. what this means for you is that if you are using some sort of marker (we used chalk-line chalk, when I was a kid), you should just contain your powder, and then put that package inside a bigger, softer container. this way your outer cover and the chalk help slow down any of the tape or other debris instead of adding to it. (this is also a good place to point out that any sort of chalk like powders you use for a marker shouldn't be flammable. flour for instance, when scattered through the air and ignited will generate a very big fireball)
4. after you think you have something that will work make up a few tests with very long fuses (or det wires, whatever you are using for a trigger), and test them in a safe spot, a 55gal drum works well. when you test them you should put some other objects in with them so you can get some sort of idea of what it's going to do to anything or anyone who is standing near.
5. measure your powder, and wrap all of them the same way. without a scale or other accurate measure you could work up a safe test but accidental use too much powder on the ones you use. consistency is incredibly important, if I learned nothing else from that stage of my life, I learned that surprises suck, they are never a happy occasion.
6. when deciding on what powder to use pistol/shotgun powder is faster burning than riffle powder, black powder is faster than either (the finer the pieces the faster it burns), flash powder is faster than all of the rest.
before you build your own you should check for other options. I'm assuming that you are going to use these among other people, this is about as far as you can get for a safe environment to set off homemade fireworks.
if you your knowledge of this stuff is limited enough that you are asking for advice on a BBS (where you can't even see how many fingers the guy who's advice you are taking has left), you should seriously think about other alternatives, and if you still plan on going ahead, consider it again, repeat this as long as it takes to talk yourself out of it. I'm only giving you what info I have because if you are determined you'll likely forge ahead without the info anyway. I'd hate to see it be any worse for lack of knowledge.
if you're not using any sort of a smoke or dust marker and just want the bang, you could probably do better to make some sort of a heavy steel shell that would hold a blank cartridge and be triggered by impact with the ground. also with something like this you could just pick them up at the end of the day, clean them and re-load them for the next day.
but again, the best advice I can give you is to not build your own. the learning curve is very steep, and the gov't isn't near as willing to look the other way as they were 25 yrs ago. I wouldn't be surprised to see someone charged as a 'terrorist in training' if caught testing this kind of thing.
or you could always just build the same ones that my friends and I used when we were kids (just kidding, DON'T). just a big firecracker (not the m-80's, just the ones that are about as big as your thumb) that had been dipped in wax until it's a nice size for throwing. we then scored them with a hot knife so they looked (and fragged) like an old pineapple grenade. they were vary reliable and you never had to listen to that whine about "you missed me", "no I got you", since the guy was usually still trying to catch his breath, and if he still tried to deny a hit you just checked for bruises.
