x64
I'm not aware of any rimmed variant of the .242 Vickers, It is a mystery until I get the rifle in my hands.

Matt
The .242 Vickers bullet diameter is an enigma. Various sources say .249" or .253". I measured an actual vintage Kynoch bullet and it was ~.247"
Now that said, my Cogswell & Harrison has a grove-groove of .255" with fairly deep rifling grooves. There is a fella in OZ with a .242 and his rifle also measures.255"in the grooves.
Apparently the standards of the day (between the wars) were no standards at all?

I size normal .25 cal (.257") cup and core 100 grain bullets to .254" with excellent result in the Cogswell & Harrison M98 Mauser

This one will get the bore(s) slugged first thing to see what I need to do.

- Mike