game last night

Ok i played call of duty all day. you what i find funny??? Is that i can light someone up with a gun and nothing happens, yet the shoot once and I'm dead!!! what is up with that.... Playing headquarters is fun but just so you know you don't level up there. oh ya any advisce on this.. you know when someone throws a nad at you , you can press r3 to throw back. Well why when i do that i still blow up?? anyone can help on this it would be great. Well going to game some more later will update you..