Here are some more detailed descriptions of how these items function in the real world.
Silencers- Various types of silencers and silenced weapons are available, but I will try to go over the basics here. The actual term for a silencer is a suppressor, and versions have been made to fit a large variety of weapons. All suppressors have a limited service life, but there are, (expensive) models available that will not "burn-out" under rapid fire. Semi-automatic fire through a suppressor should not cause a burn-out and a well made model will be able to withstand periods of fully-automatic fire. Suppressors are designed for specific models of weapons, and are generally not interchangeable. Many weapons are not specifically designed to fit suppressors, and while they can be modified, this takes time and knowledge of the process involved. While a suppressor can do a great deal to reduce noise, subsonic ammo is needed to effectively make the weapon silent. This ammunition eliminates the crack of the bullet as it breaks the sound barrier, and is available in most popular cartridges. Keep in mind that unless the suppressed weapon is something like a .22, the shot will still be far from silent, (don't trust the movies to tell you how a silencer sounds either). Wound upgrade tests for subsonic RIFLE, (rifles must be specially modified to fire subsonic ammo) ammunition are made at a -1t penalty, and ranges will be reduced for all weapons. The DL of the weapon is also reduced by 1 for the purposes of penetrating armor or other hard substances. Rifles with subsonic ammunition have a maximum range of about 300 meters, while pistols will only be affected at extreme range. Suppressed weapons without subsonic ammo will not be quiet, but won't give away the shooter's exact position. Your players should know that suppressors are heavily restricted items and carry stiff penalties if found by the authorities.
Laser Sights- As cool as they may be in the movies, the effectiveness of laser sights has often been disputed. While they can be a useful tool, a weapon's standard sights are enough to get the job done without dealing with the negative aspects of lasers. The beam can be activated through pressure on the grip to enable it to be brought into action quickly. It provides a +1t to hit, and a +2t for aimed shots within 30 meters. (Here's an idea for an interesting scene: 2 players, both with laser sights burst into an apartment. A MIB is standing in the middle of the room with a hostage. One of the red dots is on the MIB, the other on the hostage. With no time to determine where the players are aiming, who will fire?)
AP bullets- Make these very difficult to get, (they're also often illegal). The Army uses rifle caliber AP rounds which are often legal to own. You've probably come across the term "teflon-coated bullet", often used in conjunction with "cop-killer". The teflon round was another attempt at misinformation prepetuated by TV shows and movies. Many years back a company named KTW marketed a special round capable of great penetration against vehicles for law enforcement. These bullets were only sold to police and are now nearly impossible to find. AP pistol cartridges only provide a +2t to penetrate armor and are a rare collector's item. Instead of reducing the DL by 1 for AP rounds, provide a +2t bonus for downgrading damage and stabilizing. In pistols, these rounds are extremely powerful, have heavy recoil, and can damage the shooter's weapon.
Tactical Rounds- While some bullets exist that are capable of greater damage than normal, they are rare and their performance is limited. The fact is, weapon designers have been trying to come up with more lethal bullets for years, it's what they do. The key to causing damage is a good combination of penetration and expansion, which has resulted in the development of today's jacketed ammunition with an expanding point. Rounds with greater expansion and fragmentation sacrifice penetration, lowering the chances of reaching the target's vitals. Glaser safety-slugs for example, are a special type of handgun ammunition designed to break-up in the target, causing large wounds and limiting penetration, (used by law enforcement on airplanes). These rounds don't function reliably in semi-automatics, and have such low penetration that they can be stopped by a winter jacket. Hollow-Points are not tactical rounds either, and I've decided not to bother distinguishing them from Full Metal Jacket, (although the difference can be substantial, so you may want to give HP ammo a +1t bonus to damage and -1t penalty against armor). HP ammo has an opening in the nose of the bullet which creates an expanding point, (evolved from the original "dum-dum" bullet) while FMJ is a bullet entirely jacketed for limited expansion. Under the laws of war, the military can only use FMJ ammunition, but counter-terrorist teams are seen as exempt from the rule. Rumors and false claims of deadlier ammunition are always circulating, as proven by the Black Talon hoax a few years ago, but these are nothing more than media myths which have been disproven through testing. Overall, tactical rounds are unrealistic and make the already too-lethal ConX combat system deadlier.
Night Vision- There are a number of ways of firing weapons at night. The simplest is a flashlight, usually mounted on the end of the weapon. This option gives away the shooter's position, but provides no penalties to hit and many flashlights are powerful enough to blind an adversary (+2Df penalty for them to hit). Another option is to wear night vision goggles. This allows a shooter to see a large field of view without giving themsleves away. The disadvantage is that NVGs cannot see with enough detail to be used with iron (standard) sights, and provide a +2Df to hit in these cases. Special NV sights can be fitted on a weapon, including "reflex" sights, or a laser/IR beam, which only provide a -1t penalty to hit. In these cases, range is usually limited to the range of the NVGs, which varies but is often as long as that of the weapon. The final option is using a night-vision scope mounted on the weapon itself. This provides no penalty to hit, is the only real choice for sniping, but only lets the shooter see a limited field of view, and is therefore impossible to use in a CQB environment. Some night-vision scopes can also be used during the day, but they are far bulkier than conventional telescopic sights.
"Non-lethal" Ammo- There is a variety of non-lethal ammunition available, (more accurately called "less-than-lethal"), but by far the most available and popular are special cartridges for 12 gauge shotguns. These fire a spray of "bean-bags" which inflict blunt trauma on a subject. Damage is Tw2, and becomes Bk3 if used against the head. The rounds are only effective within 10 meters, and the DL is +1 if they are used within 5 meters. The ammo is ineffective against armor, and the DL becomes -1 if used against heavy clothing.
Bipods- Weapons which use bipods tend be high accuracy rifles and machine guns, both of which receive no bonuses from these devices because they are necessary to achieve the listed ranges. Other weapons using bipods receive a +1t to hit.
Extended Clips- Many different types of extended magazines are available for weapons, but the exact size and availability depends on the gun. Pistols generally don't use large magazines because they don't produce large volumes of fire, but extensions of a couple of rounds or so are available for some, (particularly Glocks). Extended clips for rifles are out there, but for the most part, rare. 75 round drum mags for AK-47's are fairly common, and C-Mag's 100 round magazine for 5.56mm rifles is definitely handy, but hard to come by. Submachineguns don't use any mags other than those listed in the weapons section, but a 9mm C-Mag has recently become available for the MP5.
Other Accessories- When referring to a weapon's accuracy, it is most often listed as "out-of-the-box". This is because many gun owners heavily modify their weapons after purchasing them to increase performance. Such adjustments may include a better barrel, ghost-ring sights, and a softer trigger pull. Such extensive modifications are generally available only to very popular guns, which have been around for a while, like the 1911, AR-15, and Mini-14. The price of these modifications can be twice the cost of the gun, and provides the shooter with a +1t to hit.