Quote: "Every FPS needs a:
shotgun (or any wide area projectile gun ie. UT's Flak cannon)
rocket launcher (or any type of explosive ie. grenade launcher, nuke)
machine gun (or any fast firing gun ie. assault rifle, minigun)
pistol (or another "weak" starting weapon)
rifle (or any really accurate gun ie. rail gun)
knife (or any melee weapon ie. HL's crowbar, UT's pneumatic hammer) "
Very true:
Unlimited Weapon : This can be either a gun that never runs out of Ammo, or a Melee Weapon. You have to give characters something when they unload thier ammo into a wall for fun then wonder why they have no ammo to kill monsters that come at them.
Weak Weapon : Traditionally this is a pistol. Usually you'll give it a reasonable rate of fire, reasonable clip size. Usually the draw back is not much power. Tend to start players off with this weapon.
Powerful Weapon : This generally is a Shotgun. Has alot of power, but reloads and rate of fire is slow. Generally the second or third weapon a character finds. Good for powerful single enemies but crap for groups.
Automatic Weapon : Machine gun, alot of games will have 2 fire modes; so secondary on these is a more powerful shot or a grenade. Rate of Fire is extremely high and holds alot of ammo, but shots generally do pathetic damage without unloading entire clips.
Ultimate Weapon : This can be just about anything, and generally is the most powerful thing players can lay thier hands on. So is hard to get. Your imagination is the limit.
[Optional]
Sniping Weapon : Name says it all. A weapon for picking enemies off from a distance.
Projectile Weapon : This comes in 3 flavours. Rocket Launcher, Grenade Launcher, Other. Rockets generally are self explanitry, Grenade launchers are well again self explanitry however you can have more fun by changing what types of grenades are available to the player. Other can be anything you throw or such at the enemy or to trap the enemy... Grenades, Floating Gun Orbs, Trip Mines, etc..
Everything else generally falls into those catagories.
The trick to a good selection of FPS weapons despite what they are, is to balance them. People will generally stick with the same weapons unless there is a benifit to using the others.
Unreal 2 for example, you get a real benifit from using the Shock Staff on heavy armour Mercs, but it's pretty crap for everything else... Shotgun is good for certain Mercs, but Machine guns are better for smaller groups. So you try to rotate your weapons based on what your up against.
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as for the gun your all talking about:

Heckler & Koch XM8 System is one of the most advanced intelligent firearms in the world. Still doesn't hold a candle in terms of reliability, ammo preservation, armour peircing, and all round abilities as the FN F2000; but it is only a H&K