The trouble with lead bullets is that on hitting an animal there is enough energy that the lead melts and then you have a column of molten sprayed into the caracass. Some of the lead will harden into lead fragments that we can find. Much will end as microscopic particles that are very easily ingested. Some of the bullet will remain in one piece and exit. How much? Well it very much depends on the type of bullet. A typical hollow nose ballistic tipped Varmint type bullet from a 22 centrefire probably most of its lead into a fox as there is minimal exit wound.
A typical cup and core stalking bullet will retain about 60 to 70% and a tough bonded core bullet a bit more.
A monolithic copper bullet works very differently. Copper has a much high melting point than lead, so it won’t melt on impact. The petals open up and you then have a flat nose spinning device cutting through the body tissues, severing and impact major blood vessels and CNS before exiting. A monolithic bullet will retain 95% of its mass, and if does shed particles those are easily seen.
Microscopic lead particles are easily ingested when meat is eaten. And in many cases, given that meat is acidic, they will be partially dissolved into lead salts before they are eaten. In any case stomach acid will dissolve lead and thus it is then adsorbed into the body. There is plenty of good science that clearly demonstrates that lead in the body is not good for you or wild birds etc.
Birds are particularly effected because they don’t have teeth. Instead they have a crop which Is a large muscular organ at the base of the throat. They ingest grit and crop is used to grind up the food. Lead shot etc remains in the crop where it too is ground up. A lead pellet will pretty much stay in the crop until it is ground away.
At least with an animal a lead pellet will probably only remain in the body for several hours as it passes through the digestive tract and is then pooed out. But it’s surface will be digested.
In man, there is now plenty of evidence that demonstrates that lead levels as low 25 nmols per litre of blood is enough to be implicated in leukaemia and other nasty cancers.
The Food Standards Agency opening stance on game meat is that it contains lead and is thus potentially harmful. Have a read here.
Lead-shot game
They state that this advice is based on a sample of consumers in Scotland carried out in 2012 who had eaten game consistently.