The Saiga-12 exists in 3 versions:Saiga-12SSaiga-12KSaiga-12S EXP-01Main differences are length (The S12K has a foldable stock) and different clip sizes.There is also a drum magazine availale which can hold 20 rounds instead of the normal 5-10 rounds.

The M16 is one of the rifles that is used by a lot games. In fact it is a pretty old weapon (see below), and more and more it is preplaced by the M4 carabine.   Deutsche Artikel: Gewehr M16 A2 (23 Photos) und M-16 Sturmgewehr The M16 assault rifle was developed after the Korean war. In 1963 the M16 A1 was manufactured, but it had some serious difficulties:1) it was not very reliable in a muddy environment 2) if a soldier used a fully filled magazin, bullets often got stuck3) a lo soldiers called it a "toy rifle" because the butt stock was made with plastic The different versions are:M16 A1: 5.56mm, full auto fireM16 A2: 7.62x51mm, stronger rifle, 3-round bursts onlyM16 A3: used only by US Navy, 7.62mm, semi and full auto fireM16 A4: mixture between M4 and M16A2, using standard mounts Clones/copies and variants: AR-15 (Colt Models 601 & 602) XM16E1 and M16A1 (Colt Model 603) M16A2 M16A3 M16A4 Colt Model 655 and 656 "Sniper" variants XM177 Colt Model 733 M ...

In Call Of Duty 7: Black Ops this weapon is called "Commando", do not mix this with the SIG551 Commando.

This underbarrel grenade launcher is called "SG40mm" in Battlefield Bad Company 2

Desert Eagle (Magnum) pistol .50 The Desert Eagle exists in a ton of different variants. You can get it with a lot different calibers, a lot of different barel lengths and from a lot different manufacturers. Here you find the most common version in video games: the .50 caliber Desert Eagle, manufactured by Magnum Industries.  

This version of the MP5 has special parts to be used at the water front. This means especially it has a better resitance against salt water and corrosion. Afaik this is not the only difference?

http://www.beretta.com/index.aspx?m=74&idc=2&ids=27 http://en.wikipedia.org/wiki/92FS

The MP5k is the short version of hte well Heckler & Koch MP5. MP5k stands for "Maschinenpistole 5 kurz" (means: "submachine gun 5 short").One of the specialities of the MP5k is, that there exists a very special version for german special forces: the MP5k sits in a suitcase and can be fired with a hidden trigger in the handle. This sounds like a cheap B-movie (or a old James Bond movie), but it really exists.

The SIG 551 Commando is a variant of the SIG 550 rifle. The changes are minimal, this si why we list both versions as one item here.

Sniper Rifle PSG-1 Heckler & KochPSG stands for "PräzisionsScharfschützenGewehr 1" (Precision Sniper Rifle 1).