3 ring bullet with all measurments what is it?

[coinhound1983]

Weight 408 grains
Length 25.37mm
Width 12.66 mm

 

[TheCannonballGuy]

Thank you for providing the precise measurements, which confirm my eyeballs-only "best guess" in your previous post of the bullet. It is definitely a US .50-70 Springfield Model-1866-through-Model-1871 rifle bullet.