.41 short rimfire?

[CPerkins]

My wifes grandfather recently gave me a box with some old ammo in it. Pretty cool full boxes of old Winchester and Remington shot gun shells. Coolest thing was a plastic baggy of old rimfire cartridges. The bullet diameter is 0.407. Tip of the bullet to the back of the case is .907 Headstamp is a "U". Looked it up and it looks to be a .41 short rimfire. 130 gr bullet alittle over 400fps. Apparently they are for an old derringer type pistol. Anyone more familiar with this than me?

 

[Wobblyshot1]

There's a pretty neat summary of rimfire cartridges in Wikipedia.