Halo 4: Weapon list's and info. (Some rumours)

Assault Rifle-
The standard UNSC Rifle. New look, same old gun you know.

Magnum-
Unknown if this is the magnum from Halo CE or not. Predicted to be in between. Same Design.

Battle Rifle-
The BR is the main ranged weapon of the UNSC forces. Same Gun you know and love. Best range weapon next to Sniper.

DMR-
The DMR is the Close ranged BR. It can beat a BR in a Close Quarters Battle. It has been slightly improved from Halo: Reach.

Railgun-
The UNSC'a Newest most High Tech Weapon. 1 hit kill.

Sniper-
The Sniper Rifle looks much different from any other Halo game and sounds stronger and more intimidating. Scope has been improved, same Damage.

Sticky Detonator-
Acts as Grenade Launcher that sticks to enemies and is the size of a magnum.

Shotgun-
New design, same gun. The standard close Quarters weapon of the UNSC

Rocket Launcher-
The Rocket Launcher is the standard Explosive weapon of the UNSC. Same as all other games.

Saw-
Brand New gun. Newly revealed by Halo Waypoint. This baby looks like an LMG (Think of COD) and shoots as fast, if not, faster than the SMG (SMG will not be returning).

Spartan Laser-
Standard AA Weapon of the UNSC. Same old gun.

MMG (Mounted Machine Gun)-
The Mountable HVG (Heavy Machine Gun) that you can rip off of it's stand (know what weapon I mean now?)

After Halowaypoints new UNSC Armory video, lot's of new little things have been revealed. There are 2 big things and 1 rumor though.
When getting a no-scope with a sniper, youvget a Medal called Snapshot. It gives you 10 points. It looks very similar to the headshot medal.
Second, there has been a leak about a Promethean Pistol. For more info on this topic, visit Ducain23 on youtube. He is one hell of a youtuber.
Lastly, there have been rumors of a flamethrower. Apparently it is Burst fire and you can hold it like any other gun instead if having to hold it low like the missile pod and flamethrower in Halo 3. I personally think thats wrong. The gun looks like the railgun and the railgun has brief fire come out of it as well when it shoots. It may have been mistaken for a flamethrower but you never know.