well it wasnt the hit detection, it was the net code.
because when i sprayed a full clip into someone, then they turned and fired twice and killed me, i would watch the kill cam.
and yep, on the kill cam, it had me aiming totally to the right side of the other guy and not even aimed on him, then he would hear me and see me, turn, and kill me.
This is lag, plain and simple. And by lag I don't mean a poor connection, I mean literally there is always latency between you and the server. There will ALWAYS be situations like this, it's not a matter of poor coding, it's a matter of the laws of physics and bandwidth.
A good connection is considered sub 50-ms, which is still way slow than the firing rate of the guns. And that's just a ping time, when actual data is being transferred, there is always significant latency.
In older FPS, hit detection was server side. You fire, and then the server reports back to you and tells you whether or not it was a hit. This delay would cause you to have to lead the target to account for the lag.
In CoD, hit detection is client side. You put the marker on the enemy and shoot, and the client then tells the server that it's a hit - the other way around. This provides the illusion that there's no lag, and it makes the game much smoother. But it's still there. A player with less latency will see you first, and will appear to have super human reaction time. As soon as they register enough hits to tell the server you're dead, then the server kills you. On your side, you may have registered quite a few hits, but if they can report back to the server that you're dead first, they win. So on their side they just completely gunned you down before you even got a shot off.
When you watch the killcam, you basically see what the server sees. Not necessarily what the other player saw. It's often very different and seemingly stacked against what you actually did, but that's the very nature of the game. I know it sounds kinda janky, but it's a vast improvement over the old server side hit detection.
The only way to solve this hit detection on your end is to get a better connection. Just cause you got 4 bars like everyone else doesn't mean your connection is as good as it can get and equal to everyone else with 4 bars, it's means it's more than good enough for a solid game. Milliseconds matter in a game like this. The faster your connection, the better.
Here's what you can do improve your "hit detection":
Get the fastest speed you can afford from your ISP
Use a router or firmware with qos, and set your 360 to have the highest outbound priority
Minimize the use of your connection on all other PCs while you're playing
Set the search options to locale only
Do all of the above, and you may even end up the host, as I often do. Then all of a sudden you're the one with super human reaction speed that's pissing other players off when they see the killcam that looks nothing like what happened on their end.