Muzzleloader bullets wouldn't have a solid base, which those bullets appear to have.
Yes, they are bullets. They are a modern type, made with a flat top to punch clearly visible holes for target-shooting, and that type is known as a "wadcutter" bullet. Do a websearch for the term wadcutter and you'll see lots of that type of bullet. The great majority are made for use in pistols. You did not tell us anything about the size of yours... but the most popular caliber of wadcutter bullets is .38-caliber, so I'd guess that is what yours are most likely to be.