The player starts with the assault rifle in most levels. It proves fairly effective paired with the magnum and will kill Elites with just 75% of a magazine, depending on the selected difficulty. It also makes an effective back up to any precision weapon (though the DMR and LightRifle are the most effective, since they cover the long range aspect of combat that the MA5D is weak at).
It is effective against lighter enemies, such as Grunts, Jackals, Crawlers and Watchers. Ammunition for it is plentiful (at least when around UNSC sources) and most Marines are armed with it.
If fired in short controlled bursts, the MA5D can have a surprisingly effective range. Pull the trigger till the reticle starts to expand, then lay off till it shrinks, and repeat. This tactic is useful for picking off Grunts and Watchers from near-precision weapon ranges.
The long reload of the MA5D is not too much longer than its short reload. If it looks like you'll need all the ammunition in the magazine to eliminate an enemy or at least severely wound one enough for a follow-up melee kill, empty the magazine.
It is inadvisable to use against higher ranked enemies; its magazine size is simply too small.
In the campaign of Halo 5: Guardians, the MA5D is the preferred starting weapon of John-117 and Edward Buck.
The MA5D's fully automatic fire makes it an effective close-range weapon. Compared with the other automatic weapons in Halo 4, it is much more versatile due to its hitscan properties and flexibility of range, though it is occasionally outperformed by these weapons at more extreme close-range. It takes 13 rounds to kill a fully-shielded player in matchmaking; ten to shields and three to the body, allowing for a bare maximum of two kills from its 32-round magazine. In close-quarters combat, it is often advisable to finish your opponent with a melee after firing at least six rounds into their shields.
The MA5D assault rifle is great as a secondary weapon to a precision weapon like the M395 DMR or Z-250 lightrifle, allowing the player to effectively occupy nearly all ranges of combat. However, like the other automatic weapons, it is not recommended for use as a primary weapon except when playing on smaller maps. The MA5D assault rifle can also be used effectively at distances approaching medium-range by firing in short, controlled bursts. Though this will drastically increase kill times, making it inadvisable against players that have already engaged the player with a precision weapon.
In Halo 5: Guardians, the smart scope ability lends itself well to the MA5D's use at mid range, giving it just enough extra reach to finish off an opponent from afar.
In Warzone, the Recon and Longshot Scope attachments, plus the Long Barrel add-on, can increase this range even further, though doing so is not exactly the most efficient use of a loadout; a Spartan would be better armed with a BR85N or M395B instead. Consider equipping the Stabilization Jets or Laser Targeter instead to allow for easier control of full-automatic fire, or Kinetic Bolts to do additional damage to vehicles. The Suppressor attachment is also a good choice for more methodical players, and when paired with proper movement management and (later) the Sensor armor mod, can let you get some quick early kills in a Warzone game. It can even do fairly decent damage to mid-sized bosses with proper aim and weak point hits.
Crouching is highly ideal for sustained fire, as the vertical recoil is reduced.
Ammunition for the MA5D is plentiful in multiplayer; players start with one in all game modes except for SWAT, Grifball, and Breakout, meaning that resupply is never an issue. It also makes an excellent replacement for an empty power weapon. If your power weapon has run dry, don't hesitate to grab the AR off the corpse of your last victim.
The MA5D now does increased headshot damage on unshielded targets. Be sure to flick up the reticle and aim for the head after the shield pops for a quicker kill.