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. It does not currently spawn in any of the original Left 4 Dead 2 campaigns.

Pros

 * Does not need to reload, so killing 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.
 * Will kill Common Infected in a single hit, regardless of difficulty. This means that, as most weapons scale down as difficulty goes up, the M60 will remain the same (much alike the Magnum Pistol).

Cons

 * The M60's ammunition cannot be refilled, so when it is out of ammo, it is discarded.
 * It is a Special Tier weapon, so it is a rare find.
 * Accuracy is average (similar to the AK-47).
 * Only holds 150 rounds, so if you don't control your fire, it runs out very quickly.
 * Ammo upgrades does not increase ammunition for the M60 like it would for all other weapons.

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.

Another way to get this is to play a survival map on any level of The Passing, as an M60 will always spawn, and you can easily mow down the never ending hordes.