I imagine it is modern but I googled: cross hatched bullet, bullet with marks, bullet with checkering, etc. and got nowhere. It obviously hit hard but it was right about .50 cal.
It is definitely a very-modern bullet, made for blackpowder and muzzleloader shooting. A similar one, but .32-caliber, is shown on the left in the photo below. The other photo shows a slightly different version as a "Great Plains" minie for blackpowder shooting. Some are "stippled" and some have "crosshatching." Larger-caliber ones have been posted here in the past, but unfortunately I didn't save a photo.