For me, one of the most enjoyable things about slingshots has been comparing all the different types of frames, bands, ammo, targets, etc. I think I've tried every single type of ammo described here on the forum, and the most biodegradable option that I actually enjoy shooting is gumballs. In Walmart a couple months ago I bought a couple boxes of "biodegradable" 6mm soft shot pellets, expecting that they'd be a nice option to shoot into the woods behind my house.
I really do not enjoy shooting the small plastic (they're too light to be accurate, and they don't make any satisfying sound), but I would have continued to use them occasionally, if only they appeared to actually be biodegradable at all.
As a test, I put 6 of the biodegradable balls in the woods, along with some copper BBs, steel BBs, and regular plastic 6mm soft shot. Over the past 2 months, they've been through hurricane Irene, some of the worst flooding rains we've ever had, hot sunny days, etc., and they don't appear to be any more deteriorated than then the regular plastic shot. The metal BBs are corroded so much that their surfaces have worn into less than round shapes - especially the ones that have worked their way into the dirt.
I'll keep this test going as long as it takes to see the metal and biodegradable shot dissolved, but I'm curious if anyone else has tried similar tests - especially if you know how long it takes a normal .177 BB to rust away to nothing. Do copper covered BBs erode more quickly than plain steel? Could I put any sort of chemical on them that could speed up the deterioration process? Thanks for any info and ideas