M60 Machine Gun

The M60 General Purpose Machine Gun is a special tier weapon that made its debut in the Left 4 Dead 2 DLC, The Passing. It carries only 150 rounds and after that's depleted, it is dropped. The Survivor will then revert back to their secondary weapon, much like with the Grenade Launcher.

Pros

 * Deals high damage, so killing Special Infected, mainly the Tank and Witch, is quicker.
 * It can mow down many Infected faster, thus making taking out a horde quicker and easier.
 * The high capacity of rounds without reloading can really help when faced with a large swarm of infected.
 * When using Ammo Upgrades if you did not use the M60 much yet, you'll get a larger amount of special bullets than you'd get with any other weapon.

Cons

 * You can't refill the ammunition, so when you are out of ammo for it, it is dropped.
 * It's a Special Tier weapon, so it is a rare find.
 * Accuracy may be diminished at longer ranges.
 * Only holds 150 rounds, so if you don't burst fire, it runs out very quickly.
 * Ammo upgrades does not increase ammunition for the M60 like it would for all other weapons.
 * The M60 does a tremendous amount of friendly fire damage on higher difficulties.

Tactics

 * Using a Bile Bomb along with the M60 can really help to rack up the kills when faced with a large amount of infected in an open area.
 * When not facing a horde or a Tank, switch to your melee weapon or sidearm to avoid wasting the ammunition on a few scattered infected.
 * Like the Grenade Launcher, it is not advised to use the Chainsaw with this weapon.
 * If possible, save this weapon for the Gauntlet Crescendo event in The Underground. It is especially effective in the narrow pipe areas.
 * During the finale of The Passing, the original Survivors may occasionally drop a M60 with Laser sight attached for the new Survivors to use. Rather than carry this weapon around while gathering Gas cans, it may be prudent to save it for the rush to the Race Car due to its limited ammo.

Achievements
An easy way to get this is by using the M60 in the sewer crescendo. At the last tunnel (Before you reach the ladder to the saferoom), a horde will always spawn and are perfectly lined up for you to mow them down.