A shortened 6mm Lee-Navy? Might have been done before... FWIW, Dutch.

What do you want to keep on the Swift case? If it's the rim there is the .225 Win and that's a lot shorter at 1.93".

I made a wildcat out of a shortened case and I had to neck ream the brass. This is not a good idea to be working with metal that had angles to it from the shoulder/neck/body junction either.

I hope I never dream up another wildcat but if I did it would use a factory case and just neck it up or down. The JDJ series used that 225 case to make a lot of cartridges. There may be a 6mm one.