BXR

Melee Fire, also known as BXR, is a button combo present in Halo 2 and in Halo 3. The button combination allows players to melee and instantaneously fire their weapon. and it is performed by pressing B+X+R. Alternatively, B+Y+Y+R can be used.

Description
The button combo works by taking down the shields first before shooting and, if aimed right, can provide an instant kill.

Halo 2
The attack works by first meleeing. Once the melee hits the opponent and does damage, the attacker cancels the remainder of the melee animation (and the delay after the melee) by pressing X. The attacker can then instantaneously open fire, without waiting for the now-canceled melee delay to elapse. The trick only works with a full magazine, however, as pressing X with a partially empty magazine will cause the player to reload, preventing them from opening fire at all; the exception is when players do not have any spare magazines remaining, in which case they cannot reload. The exception also allows players to chain BXR.

If a player has a partially empty magazine, they can press Y twice instead of pressing X once. Pressing Y switches weapons and cancels melee animations; pressing it twice switches from and then back to the current weapon. However this method will take slightly longer to do, which can be critical in battle situations. In some situation, players will automatically get a full magazine some time after a BXR, even if you shoot. This may be the result of some odd error that delays the reload (X) action.

Halo 3
Like many other button combinations, Bungie worked hard to prevent the Melee Fire from appearing in Halo 3. However, a similar combo can be used by pressing RT and B in rapid succession. By pressing RT before B, a shot is fired immediately before meleeing. It works best with single-shot weapons such as the Sniper Rifle, enabling a very fast kill. While attempting to use this trick with a battle rifle, if done incorrectly, the rifle will only fire one or two shots.

Most players, though, have adopted the B+A+R. This allows a player to melee, jump backwards and shoot a target while in midair.

Miscellaneous
In Halo 2, and when playing Halo 3 offline, an additional button combo becomes available: RT+RT+Y+B. This performs a shot followed by a melee and a second shot that, when executed correctly, fires at the unshielded head of the target. This results in a kill within the timespan of a melee.