The ACR is a fully automatic weapon, unlocked at level 48.
It started life as a design for a lightweight modular rifle platform by American company, Magpul.
Design on what was then-called the Magpul Masada Adaptive Combat Weapon System started in 2006, and
since 2008 the design has been licensed by Bushmaster as the Adaptive Combat Rifle, or ACR.
It is designed around the 5.56 by 45 millimetre cartridge, although as a modular platform can be fitted to fire alternatives, such as the larger-calibre 6.8mm Remington 'Special Purpose Cartridge'.
Although the ACR is yet to be fielded by any military force, its development does show promise as one of the potential replacements for the venerable AR-15 derived platforms currently in service today.
In game, the ACR is a low-damage, low recoil weapon when compared to the other assault rifles.
The M4A1 and F2000 share the same damage with the ACR, but the ACR has the slowest fire rate with the lowest recoil of the three.
This means the ACR is very effective at long range - despite dealing minimal damage, you can reliably hit a target with automatic fire at a considerable distance.
A sniper's bane, and pretty deadly at most other ranges too - the ACR retains near pinpoint accuracy however far away your target lies.
For your blue perk, Scavenger is a sensible choice to allow you to be more liberal with your trigger finger - this is especially useful if you're using FMJ.
The ACR is relatively weak up close, particularly if you're taken by surprise - so you should take care to avoid areas best suited to close quarter combat.
You can bolster the close-range ability slightly through the use of Sleight of Hand Pro - the faster aim speed might give you the edge - but given that you can easily run out of ammunition with the ACR I'd consider Scavenger to be the better overall perk.
For your red perk, Stopping Power is the logical choice - while the accuracy of the ACR means it's easy enough to hit a target multiple times, the low damage at range can be an issue in a long-range firefight.
You could run Hardline, or Cold Blooded - and in most firefights you might come out OK - but there's nothing that quite compares to Stopping Power as far as general usefulness is concerned - and in equally matched firefights you'll be at a disadvantage without it.
For your third perk, as usual for an aggressive and mobile loadout such as with the ACR, Ninja Pro will conceal your position and allow you to move near enemies undetected.
Steady Aim is also a solid choice, permitting more effective hipfire which may assist up close.
Your secondary may be the more reliable choice, however - and my preferred pairing with the ACR was a pistol, for the fast draw speed.
With Scavenger and a relatively versatile primary you won't need to fall back on a secondary in most situations - so the fast switching pistols become the most useful secondary category.
All the available handguns will kill more quickly than the ACR at close range, so they can really help fill the void should you become overwhelmed at close range.
My preferred pistol with Stopping Power is the M9 - the USP .45 is very similar, but I prefer the M9's sights and improved magazine capacity.
Should you be caught in the middle of a reload, a quick switch and a double tap might just make you glad that you decided to pack a pistol.
The ACR is a very competitive member of the assault rifle category, largely due to its ability to accurately place automatic fire further out than any other weapon.
The damage is low, but if you land four or five shots in succession you'll kill at any range in about a third of a second.
The only real downside to the ACR is the close-range performance; The shotguns, high-damage assault rifles and SMGs will all fare better.
Still, you can engineer the engagements you face to avoid situations where you might be vulnerable. Steer clear of high-traffic interiors and instead seek longer sightlines. Be wary of snipers with the same idea - although if you can spot a sniper before he spots you there's a good chance you'll be able to pick them off, or at least prevent them from getting an accurate shot before you get to cover.
With precision unseen ouside of the sniper category, the ACR is a hard weapon to go wrong with.
As long as your aim is accurate and your awareness of the enemy's position is keen, you'll find the ACR is a very effective weapon.