It was Lapua brass. I've fired approximately 16,000 rounds with this action and bolt (on barrel 3 now) with the same load and same primers and this is my first issue.
I took it to the gun shop where I got it almost 8 years ago this afternoon, they gave it the once over and declared it good but did say that if it happened again, they'd replace the firing pin free of charge just to be sure.
I'm no CCI fanboy but they are always available to me and have always worked.