THE M67 Fragmentation Grenade
Using the M67 Frag Grenade in AAO is relatively easy. All you have to do is pull it out and throw it by pressing the fire key and releasing it. 4-5 seconds later it will explode.
Cooking a grenade is one of the coolest things to do to surprise your enemy. When you cook a grenade you are pulling the pin by pressing the fire and alt fire keys and holding the live grenade in your hand for a few seconds before you throw it by pressing the fire key. Usually the opfor you are throwing it at can hear you cook the grenade and run away, but if you pull the pin before you are close to them they won't. A good rule of thumb is only cook it for 2-3 seconds because sometimes grenades will have shorter fuses than others.
We have all seen the kamikazes who run into a room known to have opfor in it with a grenade in their hand. The proper way to do this is to cook it long before you enter the room. The opfor will know you have a grenade in your hand due to how you look. The more the cooked the better chance you have at taking them out with it.
Airbursting a grenade is a great technique to use to kill an Opfor hiding behind an object. You cook the grenade like normal, but you throw it higher so that it will explode in the air over your target.
Silent grenade throw
If you want to throw a grenade without yelling frag out, all you have to do is press the slow walk key before throwing it and you will not yell "Frag Out".
Although you have no cross hair when throwing a grenade, you can aim it by lining up your middle finger and using that as the crosshair. Remember, the further you throw it, the lower it goes.
Rolling frag grenades helps a lot when trying to clear a room, because they tend to do what the flashbangs do, go hide in a corner. When rolling a frag grenade, try to aim for the middle of the room or structure you are clearing.(its best to have 2 people doing this, 1 rolls a flash and quickly gets ready to enter, the other cooks off a grenade and rolls it in, and the flasher moves in and clears. Repeat this process several times.) Also, when frags are cooked off in the rolling process, cook them off a little bit shorter than you usually would, because rolling takes a hair more time than throwing.