old rimfire cartridge identification please

[Rrickoshae]

can anyone help identify this round please? The case is copper, rimfire and the heastamp 'U'. The case is 38mm long, the base dia. is 15mm and the calibre is about 10mm - I don't have a micrometer so can't be too precise. I have shown it on its own and against a Spencer 56-56 for scale. I guess its an American calibre.
thanks, dave

 

[bdgreen]

Probably (?) a .41 Swiss by Remington-UMC, their version of the 10.4 Swiss Vetterli.

 

[Rrickoshae]

yep, I reckon thats it. Many thanks again bd, that's all todays queries sorted. Many thanks, Dave