In MW2 FMJ was awesome. It allowed you to penetrate objects you couldn't without it, retained more damage while doing so, and there were plenty of common locations where it worked.
In BO, it came back as Hardened, but seeing as it competed with other good perks, it saw little use.
In MW3 it showed up as Impact. It seemed useful, but there seemed to be very little locations where you were able to penetrate something. Even with the few that were somewhat common, you could usually get the kill without using Impact.
I'm curious to know if anyone has any information about what it can and cannot penetrate in this game. Does it actually allow you to penetrate objects you cannot when not using FMJ? What is the damage retention? --- "We do not stop playing because we get old, we get old because we stop playing." -- George Bernard Shaw
Annoyingly useful. Unlike MW3, bullets actually go through walls in this game without FMJ, with FMJ you'll swear it's lag compensation, but upon watching the kill cam you'll realize the ****er just pumped a wall full of lead and got you. Thankfully, it can't be used in conjunction with MMS.