Drsancho, if you really-really want to know the specific identification of the bullets you found, you'll need to very precisely measure their diameter, in hundredths-of-an-inch. (For example, .52-inch.) You'll need a Caliper for that kind of measuring. See the photo, below.
If you don't want to go to the effort of using a Caliper, you COULD just put a ruler up to the bullet's flat bottom, and make as close an estimate as possible. But please keep in mind, being off by even as little as 1/32nd-inch can change a bullet's ID. For example, there are .36-caliber, .38-caliber, and .40-caliber bullets. So, saying it's "about" a 3/8-inch in diameter (.375-inch) isn't accurate enough to correctly ID your bullets.
A US penny is very close to .75-inch in diameter. To my eyes, your bullets appear to be larger than half (.375") of a penny's diameter.