M249

The probability for finding this per attack heli (4 x Elite crates at 6% probability per crate) is not 25%; it is 21.9%. Probabilities don't "add up" like that (6% * 4 = 24%). To calculate the probability of finding at least one of a given item, use the following formula:
P = 1 - ( per-chance probability of NOT finding the item ^ number of chances )
For the M249, the P of NOT finding it is (1 - 0.06) = 0.94, so the formula is: P = 1 - (0.94 ^ 4) = 0.219
To get a 50% chance of finding at least 1 M249, you'd need to encounter 11 Elite crates. Doubling this number will *not* guarantee you find one! The probability asymptotically approaches 1 the more chances you get.

The M249 can shoot exactly 2,000 rounds of any ammunition before breaking while in mint condition.

1. The M249 has a high recoil movement penalty, staying still will make the gun much easier to spray at longer distances.
2. The simple sight is a good mod for the M249 with the benefits of more visibility when aiming down and the higher sensitivity the mod gives.

The M249 is very good at destroying the Patrol Helicopter.

One of the weapons of preference for roof campers, with a fat zoom scope attached, and tapping/bursting.
To deal serious damage to such roofcampers, climb up after killing them and steal the M249 with ladders or a build-in; their rarity will make them cringe.

Given auto-turrets can now hold guns, it is a great investment for loot rooms. Given its ammo capacity and dps, it will often drive off even small groups if in the right position and properly protected. This should not be used on external turrets however given it is an easy target then

Slap an 8x scope a laser sight and a silencer on this and you'll melt people.

Amazing weapon, if you can actually get one. The chance from getting one from each helicopter taken down is 25% so kill the heli 4 times and you will get one are two if you are lucky. Overall good, but way too rare.