Take a set of inch calipers and tell us the exact diameter....weigh it in grains.
First guess is.....it looks relatively modern. If its .450-.454in diameter it looks to be about 378-475 grains. Originally designed for the 45/70 cartridge this bullet may also be used in the .458 Winchester..
TiredIron
We'll await your measurements and weight........ A couple of clearer pictures would also be beneficial, and I'm assuming you came across this somewhere in Texas..??