RE: Tree Sap Bullets
The wooden bullets, which someone mentioned, were tried by the Japanese, out of desperation. The ones used were fitted with a metal cap on the base, in an attempt to try to keep them together. They didn't always make it to the target, let alone in one piece. Also, they had to be used in a special, lower velocity load, as they would not stay intact if fired at normal rifle velocities. This, of course, heavily compromised the ballistics and effective range of the weapons being used with them. All in all, not a very satisfactory result...and hardly practical for standard use.