From Halopedia, the Halo wiki
The M45 Tactical Shotgun (formally Tactical Shotgun, 8 Gauge, Pump Action, M45) is a shotgun manufactured by Misriah Armory. The M45 is commonly used by the United Nations Space Command alongside the M90 Close Assault Weapon System, a functionally identical copy designed by Weapon System Technologies.
The M45 is used during most close-combat scenarios (particularly in urban areas with heavy enemy occupation), as well as in boarding actions. It was used in numerous military operations in urban terrain (MOUT) situations during the Insurrection and was met with widespread acclaim by its users. The M45 later saw widespread use during the Human-Covenant War.
The M45 shotgun features a dual tubular, non-detachable magazine and is chambered for 8 gauge ammunition. The base model and the M45D may be fed up to six shells whereas the E variant accepts twelve. It is a special-purpose weapon used in any situation where the range of engagement is limited and when over-penetration is not desirable, but maximum stopping power is required. Some variants of the M45 shotgun feature a smart-linked controllable choke.
M45D Tactical Shotgun
The differences between the M45 and the M45D are mostly cosmetic, as the M45D retains the standard six-round internal magazine and firing mechanism. The M45D is unexpectedly comfortable to fire and simple to control, despite the shotgun's powerful 8 gauge cartridge and light weight. This is due to the M45D's magnetorheological recoil dampening system, which is considered very under-appreciated. The M45D shotgun does not feature a smart-linked controllable choke, unlike some M45 variants.
M45E Tactical Shotgun
The M45E boasts greater stopping power than the standard M45 and has a twelve-round internal magazine rather than the standard model's six-round magazine. It features blue iron sights instead of the red sights common to the original model, though it is otherwise superficially identical.
There are also several variants of this specific model:
Due to the M45's popularity among UNSC service members during the Insurrection, Weapon System Technologies opted to design a more affordable and more practical copy of the M45. The resulting M90 Close Assault Weapon System is part of the DTM series, which is marketed to the military, law enforcement, and civilians. The standard model of the M90 Close Assault Weapon System is functionally identical to the M45E, possessing a twelve-shell internal magazine, as well as matching the original in range, shot spread, and stopping power. The M90A is based on the original M45 Tactical Shotgun and performs almost identically, despite its longer barrel; it too features a six-round internal magazine. Although the M90 has since dominated both the military and private sector, it is common for UNSC personnel (particularly Marines) to use both weapons concurrently.
The M45 shotgun is more powerful than the M90A from Halo 3 and Halo 3: ODST. The pellets have a tighter grouping and the range is superior as well, which also makes it harder to hit multiple enemies at close range. Although this change is hardly noticeable, impact force can be noticed as damage is higher.
The shotgun is very powerful in small confined maps. It should be used as a "corridor sweeper" because of its extreme damage at close range. The Halo: Reach version also has more recoil than its Halo 3 counterpart.
Halo: Combat Evolved Anniversary
In Halo: Combat Evolved Anniversary, the M45E is used in lieu of the M90 CAWS featured in the original game. As the changes between the original weapon and its replacement are superficial, the weapon performs identically to the M90 in Halo: Combat Evolved. The weapon model uses the M45 Tactical Shotgun seen in the Halo: Reach Beta.
The M45D Shotgun, according to 343 Industries employee Chris King, has "a lot longer range now, less damage falloff, and is quite a bit more powerful than say the Reach version overall." In terms of relative firepower, the shotgun is a one-shot kill weapon and should be used for close encounters. It is notable for penetrating enemy shields, particularly Elites, and it takes only two shots to kill a Promethean Knight.
Halo 5: Guardians
The M45 operates similarly to its Halo 4 counterpart, with a few additions; like all weapons in Halo 5: Guardians, it can be smart scoped to increase its accuracy (in this case, tightening its pellet spread with a trade off of increased recoil), its base range is increased, its magazine has been reduced to 5 rounds instead of 6, and its tactical flashlight (previously just an aesthetic part of the weapon's design) is continuously on. The shotgun still features the problem of pellet inconsistency, though, making it ineffective for engagements past 10 meters (33 ft), where the similar but non-hitscan Scattershot may be a better choice. The M45 is the preferred weapon of Kelly-087.
Halo: Spartan Assault and Halo: Spartan Strike
The M45D Shotgun has an extremely short range though significant spread; however, it inflicts massive damage at point-blank range, enough to kill an Elite Major in one shot. The weapon's ammo is capped at 30. Due to its extremely short range, it is not recommended to fight Brute Chieftains with this weapon.
List of appearances