determining the bullet caliber?

[canes2016]

Recently found this old bullet, looks to be three ring but have not been able to figure out the type, perhaps the era it was commonly used as well....any guidance would be greatly appreciated.

 

[mirage83]

Looks to be a modern (post CW era) cast bullet, maybe 45-70 or one of it's cousins. If you have or know of someone who has a set of micrometers or calipers we can probably narrow down the specific caliber pretty close if you measure the base area where it's not mushroomed.