The exact usage of machine guns depends on player preferences. While some prefer to only use machine guns against Mambulls and Bosses, other players may prefer to use this as their primary weapon in the alien swarm if they can afford to consume large amounts of ammunition.
Because of its large speed penalty, usage of gatling guns as a main weapon in PvP is less common, since mobility is important when fighting human opponents. Furthermore, all machine guns have a delay (spin-up time) where you must hold the fire button (the right joystick) for 1 second before it begins firing. However, the weapon's effectiveness may be considerably increased if you are skilled at quick-drawing (switching to a machine gun while firing from another weapon, thus bypassing the 1 second spin-up time and immediately unleashing its bullet storm.)
One machine gun is in Star Warfare 2: Payback: the DD2C Whirlwind.
Rank 1 POW: 120
Rank 8 POW: 420
"Nice power and high fire rate, exhaust your energy in no time."
A basic machine gun in the shop. It's fast fire chews down the enemy's health in no time but it's not the most energy efficient weapon in the game. It is also very heavy, so it's best to bring another weapon without any speed reduction. MCP-76 is useful for killing the Mantis, Poison Pit and possibly Siegfried.
MCP-76 is unlocked at rank 3 which is around the start of the game. Even so it's pretty pricy at 400,000 gold, it can be used until around rank 6.
Rank 1 POW: 200
Rank 8 POW: 700
"You are the terminator, sir."
The M-27B1 is the main boss fight weapon for free-to-play players who do not wish to spend large amounts of in-game currency. It is a well-rounded, reliable weapon with good DPS rates; when fully upgraded, it is efficient for bosses from from Mantis to Serpent. However, fighting the X-MAS Surprise boss with this weapon is considerably more difficult. The M-27B2 carries a -2 SPD penalty and chews up ammo rather quickly.
Rank 1 POW: 275
Cost: 320 mithril
Rank 8 POW: 962
DPS: 5,659 -- Pumpkin damage is estimated to be equivalent to three Black Stars rockets. Buzzsaw damage accounts for 8% of the M-Z7B2's base POW. (Rank 8)
"If you're strong enough to pick this up, then you got the ultimate."
This weapon is considered by many to be one of the top 3 strongest weapons in the game. It costs 320 mithril, which ties with the Laser Cannon as the most expensive single item to buy in-game. The M-Z7B2 not only shoots bullets, but also deals damage from both the saw in front of the gun and the pumpkin projectiles that are occasionally launched. The M-Z7B2 has a significantly higher DPS than the M-27B1, without even including the damage of the buzz-saw and pumpkins (which are slow-moving, rocket-like projectiles that are randomly fired and deal damage equivalent to three Black Star rockets). The buzz saw is especially dangerous and deals tremendous amounts of damage at close range. Though the actual DPS of the saw is unknown, it is enough to instantly kill any common alien (Digger, Stalker, Green Lady, and Tacorlion) in any PvE level on contact when maxed out. The buzz-saw damage is directly proportional to the amount of players there are in a game. When used properly, the M-Z7B2 is easily able to take down any player in a PvP round in mere seconds.
This weapon is especially good for PvE/boss battles, but demands an extremely large amount of ammo (consumes 470 energy per second) in return for its very high DPS.
All three weapons have a slight one second delay before firing because of their warm-up time. Similar to the Laser Cannon, this warm-up period can be bypassed by quick-drawing the machine gun from another weapon. The MZ is also the most expensive to upgrade. By the time you're done, you'll have spent 52,800,000 gold to max out M-Z7B2, plus the 320 mithril required to buy it. M-Z7B2 is the most expensive weapon in the game (if the upgrade costs are included).
The machine gun makes an excellent general purpose weapon, mostly in boss battles (if you don't mind buying energy or have the X028-FREEDOM bag) because of the massive DPS rates. The damage rates of the M-27B1 or M-Z7B2 is capable of chewing down HP of a boss more quickly and efficiently than most weapons. In PvP, it is recommended the Machineguns do not serve as the main weapon due to the speed penalty crippling your movement. The Machineguns are especially effective if staying put, suitable for a team-support role, delivering suppressive fire for your teammates to advance. The M-Z7B2 also has a saw under the barrel that is not only for consmetic purposes, but also can damage enemies, even when the user is dead. Another thing to note about the saw is that it holds the largest DPS in the game when the gun is warming up and shooting, and can kill a full Phoenix without even firing off projectiles. Therefore, it makes the M-Z7B2 an ideal all-ranged weapon. The combined damage of the saw and the bullets themselves grants the M-Z7B2 an upper hand in close quarters combat. It is not advised to use the saw frequently in PvP, as there is a glitch where about 40% of the time the saw kill will be rewarded to another person (no matter which faction). Until this is fixed, it is not a good idea to use the saw as a main weapon for PvP. Machine guns are also highly effective in killing players with high-tier armor, provided that you can hit the target. Even though they slow you down quite a bit, they are still one of the most solid weapons in the game. The MZ's saw can also kill target glitched aliens. For more info, see Glitches.
M-Z7B2's description labels it as an "M-Z7B2" instead of a "Machinegun." This is most likely an oversight from Freyr.