I've used AmmoSeek a few times when I was hunting for some 9mm and .223 ammo. It's pretty handy since it aggregates prices from a lot of different retailers in one spot. I've found the prices to be generally competitive compared to the other websites I usually check, and it saved me some time. Just a word of caution though: make sure to check the seller ratings and reviews before you buy. I had a minor issue with one seller not shipping my order on time, but overall, I'd say it's legit. Just be careful to avoid those sketchy-looking listings with crazy low prices; they're usually too good to be true.