Interesting observation. If a bullet was fired, would tallow or beeswax be "burned off" (in some way eliminated) due to travel down a barrel filled with super heated gases, possible friction with the barrel, friction from the air it traveled through, friction with whatever it impacted with, and exposure to the elements? If so, what attracted animals to it to gnaw on it? Since we are talking animal modification and not human, with respect to nibbling, we are also talking animal sensory systems. Is there something about lead that animal sniffers might pick up that human sniffers do not?
If a bullet was dropped, how long would the tallow or beeswax remain to attract animals to gnaw on it? I haven't dealt with that many chewed bullets but it seems to me that all gnawed bullets I have noticed appear to have the same patina on the gnawed parts as the rest, indicating that the gnawing was done early-on and not decades after the bullet was exposed to the elements. Is this the case in general? If there is something in lead that would attract animal sniffers is it masked by oxidation? If not, wouldn't most dropped bullets have indications of being gnawed on (having been left in the environment for over 150 years for animals to find), or at least a lot more that we see?
We should also take into consideration what animals are chewing on bullets and whether or not these animals would be attracted to tallow, beeswax, or some other substance and what types of bullets are being chewed, caliber, make, model? There may be some unknown information about small arms ammunition or wildlife biology involved that we could find out.