Inspired by commercially available ammo that is prefragmented for maximum killing power without overpenetration, I set out to make my own from commonly available materials. This is actually quite easy. Here's a video that demonstrates my ammo, followed by additonal insight below.
Pretty cool, huh? For those who dont have high speed internet, you'll need a candlewarmer, a old bowl to melt wax into, a source of wax such as old candles, and BBs. You'll need a piece of the material you use for your airgun barrel as well as some vegetable oil to prevent the round from sticking. Use a razor blade to shave the wax into the bowl. Once you have a good pile of shavings, set the bowl on the candlewarmer to melt the wax. While the wax is melting, take the piece of barrel material (should be as long as you want the ammo to be) and grease the inside of it with vegetable oil. Place it on a piece of glass or plasic that is also greased up. This is your mold. Pour a bit of wax into the mold and let it cool a couple of seconds. Drop several BBs into the mold, leaving a bit of room at the top. Slowly pour wax into the mold, filling the gaps around the BBs and filling it flush with the top of the mold. Place your mold in the freezer for a minute, and you'll be ready to pop out your prefragmented round.
Some Insight and Experience
I havent hunted with this ammo, but inspite of being unstabilized, it was pretty accurate out to 20 yards. The ammo I made weighed 120 grains and traveled at 425 fps in a simple sprinkler valve airgun. To test it's penetration and fragmentation, I placed a piece of 1/2" plywood 20 yards out. Behind the plywood, I placed a large cardboard box to see the spread of the BBs. The shot punched through the plywood with ease and scattered all over the backside of the cardboard box. It had enough energy to penetrate the cardboard, but not enough to mess up the bark in the tree behind it. From this experiment, it appears to be fairly lethal, yet solves the overpenetration problem. This would be a great type of ammo to hunt in urban areas.
To improve accuracy, I did use tail stabilization in a couple of rounds. To do so, take a small nail and embed it in the center of the first layer of wax. The nail should be long enough to be able to tie a yarn tail to the end of it when the round is finished. Proceed to make the round as before. When the ammo has cooled, tie on a yarn stabilizing tail as seen in some of my dart construction pages. This will enable the round to fly straight at the slight expense of adding a bit more drag.
You can experiment with using something beside BBs. Fishing sinkers or lead shot will yield heavier ammo. Small nails or brads would be pretty wicked. Hope you have fun with this idea, be safe, and use all info for academic purposes only.