I think the confusion stems from the fact that a large number of agreements are commonly balled into the 'geneva convention' term. For instance, the ban on using explosive rounds against people comes from the Saint Petersburg Declaration of 1868 (ie Declaration Renouncing the Use, in Time of War, of Explosive Projectiles Under 400 Grammes Weight).
The "I'm not shooting him, I'm shooting his equipment" issue comes from the fact that explosive shells under 400grams can be used against equipment and material, just not persons. There is debate as to whether the 400grams (just about 1lb) covers the projectile alone or the entire cartridge. If the latter, then I believe .50cal rounds used by some US snipers may be a violation. That is IF the US had been part of the convention, which is wasn't. So US snipers can legally do what for a Brit or even Canadian sniper would be a war crime.