Search:

https://support.leeprecision.net/en/knowledgebase/article/replacement-o-rings-for-rifle-quick-trim-dies

What do ya know! 12mm

Yeah be doing that next time, with the pen. It was not a lot but it really stuffed it.
Thought I had it sussed with a 10mm x 2mm but thats not worked. might have to try and get a 11mm one.

Our...

So I did a bit of a boo-boo yesterday while trimming up some 7x57 brass.:O_O::O_O:
Had done some load work and wrote the load on some sticky tape and stuck this on the rounds in question. Cool idea...