Mike & Huvius,

Looks like you have rifles marked 450EX and 360EX, and neither is in what I thought was the most prevalent chambering for those markings (450bpe or nitro vs .500/450. Or 360BPE or nitro vs 400/360.)

I really need to stop assuming that an express proof marking tells more than just the bore. I guess it refers to the class of firearm being proofed, if I read correctly the pamphlet Mike kindly shared.

Regards,
Chris