My understanding is that if tossed into a fire, it’s generally the shell casings that become the projectile, due to having less mass than the bullet.
“When small arms ammunition is burned, cartridge cases may burst open and bits of brass may fly about, but not with any great velocity, and usually not with force enough to be dangerous to life. The bullets generally have even less velocity than the brass cartridge cases, and it is necessary for the powder to be rather strongly confined to develop any velocity in a bullet. The Sporting Arms and Ammunition Manufactures’ Institute (SAMMI) reported a demonstration made by taking a large quantity of metallic cartridges and shotgun shells and burning them in a fire of oil soaked wood. The cartridges and shells exploded from time to time, but there was no general explosion of throwing off of bullets or shot to any distance. … The test showed that small arms ammunition when subjected to fire will not explode simultaneously but piece by piece, and then the material of which the cartridge and shells are composed will usually not fly more than a few feet.”
Subsequently, NRA staff conducted similar tests and surrounded the fire with cardboard. They found that neither the cases nor the bullets that flew any distance had enough energy to penetrate the cardboard.