Okay, due to popular demand, here’s a better pic. (I would have had it up yesterday, but Costco screwed up my camera downloads and I had to go to Kinkos this morning to get something I could post.)
As mentioned previously, it is a factory cartridge. If you want hints, they’re in the two posts below. Guesses so far are in comments to the original post. Check back tomorrow morning for the answer.
I’m going to say Remington 17 Mach IV. (I’d have said Rem Fireball, but someone already guessed that one)
Looks kind of like a .243 WSSM to me.