Here is some info from the official site about the weapons. I will make a few interjections in the blue text:
"For the duration of hostilities on Skira Island, you will wage war with the most technologically advanced arsenal the USMC has ever had. In the field, you will find that each weapon can be customized in response to the evolving combat scenario. Scopes, like the Advanced Combat Optical Gunsight (ACOG)(Which is manufactured by Trijicon) and Thermal Infrared Goggles (TIG), can be used to overcome adverse combat and environmental conditions. Don't forget other force multipliers like grenade launchers, smoke and night vision devices. Keep the limitations of your gear in mind too: a missile attack, while highly effective against an entrenched enemy position, kicks up a lot of dust and smoke, impairing your vision.(I have yet to have a bunch of dust kick up in my face unless they mean an artillery strike.) And when all else fails, the option to call in heavy artillery or air strikes is usually available.(You rarely get artillery support in the game. Which is pretty sad because the visual effects of it are absolutley spectacular.)
It is critical that you familiarize yourself not only with USMC weaponry, but its ammunition and subsequent stopping power. Every bullet type is designed to be effective against different materials, whether it's a flak jacket or tank armor. As you will recall from basic training, a projectile's ‘drop off' rate and environmental effects must be factored when attempting a long-distance shot. During a firefight, look out for tracer fire; this is a good indicator of the enemy's position. Remember, if an enemy bullet fails to make contact, it can still ricochet off a hard surface, causing injury or fatalities.(I have not had a ricochet hit me or my men as of yet.) This is worth bearing in mind when looking for cover.
While serving on Skira Island you and your fireteam may sustain injury from projectiles and/or explosives.
Remember, whether it's a simple scratch or as severe as a missing limb, all injuries will result in blood loss, impairing combat effectiveness. Secondary effects can include blurred vision, lapses in consciousness, impaired movement and, eventually, death. It is crucial that during or immediately after an attack, you check every Marine's clothing for blood loss. This will alert you to an injury's location and severity. Prompt application of a field dressing can save lives.
Skira Island is 220km2 of diverse, sometimes inhospitable terrain. In order to traverse it quickly, you will need to command a host of different vehicle types. Whether travelling by land, sea or air, you should be mindful that distinct vehicles perform to varying degrees on different terrain. Each vehicle allows for multiple crew positions, ensuring that your squad uses each weapon system to optimum effect. Whether you have had field or simulated vehicle experience, each control scheme and interior should be familiar and easily navigable."
Chinese "Queen Bee" SAM
FN SCAR-H- Variants include: AN/PVS-4 Optic(This is basically a night version of the Trijicon ACOG. It is good for the same distances as one, but it is hard to use for CQB)
FN SCAR-L- Variants include: Aimpoint(Good to about 150 meters, but hard to hit anything past that, due to the game having realistic bullet drop.
M16A4- Variants include: EOTech Holographic Weapon Sight(CQB), Trijicon ACOG(Medium Range- out to 600 meters), Iron Sights(Good for ~150 meters, but very inaccurate past that), Iron Sights plus
M203 Grenade Launcher(Grenade Launcher is good for taking out groups of infantry as well as light vehicles)
M4 Carbine- Variants include the same as the M16A4.
FGM-148 Javelin- Cabable of wiping out any vehicle in game or in real life this is an extremely advanced and deadly weapon. It is a tube-launched missle, which can do top attack for armored targets or direct attack for buildings and other fortifications. Each missle costs $80,000 to produce.
SMAW(Mark 153 Mod 0)- This is currently U.S. Marine issued as a medium anti-armor weapon. It is ear-splitting loud at 187 decibels, which can quickly cause hearing damage.
Some people have wondered what the long and slim shaped box is that is on many of the M16 and M4's in the game. That is known as the AN/PEQ-2. It emits two infrared-lasers. One is known as a wide beam which is used to illuminate objects. The other is a narrow beam which is used to point at targets(such as people) like a regular laser. These beams can ONLY be seen with night vision goggles, as they are infrared, which I mentioned above. This device is part of the SOPMOD(Special Operations Peculiar Modification) kit.
SOPMOD is used by SOCOM as an accessory kit for the M4/M16. However, this is becoming increasingly popular with all branches of the U.S. Armed Forces, U.S. Law Enforcement, and even civilians as SOPMOD components can greatly increase the effectiveness of the M4/M16.