To Spectral Jester and Matt, you quite obviously have no idea what bloom actually is or what is designed to be used for in the Reach blam! engine. Every Halo game had it's weapon draw backs if you spammed the trigger. For instance...
Halo 1: Pistol. squeeze off more rounds than once every 2 seconds and the fire staggers (across multiple markers)
Halo 2: Sniper rifle: Squeezing off rounds consistently caused the screen to take an upward Z vector
Halo 3: All of the above apply.
Halo 3 ODST: SMG: You can clearly see the accuracy drop when using non-controlled non-short bursts.
Halo Reach: DMR: Firing more than one round every complete second or 2 causes staggered fire.
Definition for Bloom as used in Halo: The visual representation to allow players to physically see the rate and spread of a weapons fire after a designated amount of rounds in constant fire have been reached. Again, every Halo game has this. Halo Reach was just the first one to give the player a way to really see it without having to be a highly skilled player to determine or memorize the changing of firing for weapons.
Ok, now for the whole hitscan weapon thing. First off, it is best to describe for those who have no idea what is, what exactly it is.
Hitscanning, is when the game engine does a series of calculations before the firing weapon actually ejects it's round. When you pull the trigger, the game determines the path of the projectile assuming that said projectile has an infinite velocity, and calculates what objects are in it's infinite path.
Halo 2 is the only game to date to truly incorporate the "hitscan" type weapon. And even saying that is not accurate. There were certain instances where the hitscan style of projectile use did not function as intended. There would be times at which you fired the weapon, and only 1 or 2 rounds actually would hit the target. This is because the battle rifle fires 3 rounds, but each round actually ejects at different times. For true hitscan, the weapon can only fire 1 round at a time. Which is why saying the battle rifle was a hitscan weapon, is still not completely true.
Now I do not believe hitscan has any business being in any fps. Trying to justify it in game environments that utilize such realistic collision detection and physics handling is just silly. If they do intend on doing it, then they might as well just not do any type of multiplayer. If true hitscan weapons are used, then no matter how much you stafe, roll or evade, the shots will always hit their target. Part of the magic of multiplayer is leading your opponent.
As for the realistic end of it, there are not hitscan weapons in real life. every firearm fires projectiles at a set speed determined by how much gunpowder or magnetism is present in the round or barrel. Everything slows due to physics and gravity. So why add such a silly thing into a game that uses such advanced environmental handlings?
Sorry this ended up so long, I just get really aggravated when people who do not know how the game engine works, or what data is present in the tag sets of the maps and resource files.