Need help with button and bullets

[BenVa68]

Found these today. I have found everything from the Civil war to modern items at this location. It's out in the woods. The button was a few feet from where I dug 2 Williams cleaner bullets. The casings are .22 cal. The bullets are .20 cal. Thanks for looking.

 

[FreeBirdTim]

The casing with the letter "U" was manufactured by the Union Metallic Cartridge Company, who merged with Remington. Hard to get a precise date, but one website stated that the letter "U" stamping was discontinued in 1961.