- "Seven hundred rounds, two minutes of continuous fire? I approve."
- — Robert McNamara, when obtaining the weapon from the Mystery Box in "Five".
The HK21 is the secondary starting weapon for Hudson on the level "Rebirth." It is very powerful and usually kills in one or two shots to the torso, and has the ability to gib most enemies. It can also be found in other missions, such as "Numbers" and "WMD". Rarely, it can be found with a Round Drum, which gives the player 80 rounds per drum, making for a very effective weapon. In WMD, it can be picked up from dead Soviet soldiers
The HK21 is unlocked at Level 2 to the player, as part of the default LMG class. It is also automatically unlocked in Create-a-Class.
The HK21 has the regular damage of LMGs: it will kill in two headshots, or three body shots, at any range. This damage makes it a one-shot kill in Hardcore at any range.
The accuracy of the HK21 is questionable. The iron sights are somewhat bulky, but the recoil is the lowest in its class. The moderate rate of fire at 750 RPM, coupled with its impressive centerspeed, makes the recoil very controllable. The use of an optic can greatly affect the player's handling of the weapon. Overall, the HK21 is a very accurate weapon statistically.
The HK21's handling is rather poor, along with the other LMG's. Aim times are very slow, and the hip-fire is mediocre at best. In addition, reloads are painfully long, and can be quite commonplace with the small 30 round magazine.
The HK21 gains the usual assortment of attachments in its class. Extended Mags makes a 60 round drum magazine while still retaining the same amount of ammunition, allowing HK21 users to shoot for much longer before having to reload. If an optic isn't needed nor wanted, Extended Mags is, by default, the best attachment option.
The usual optical attachments are on the HK21 as well. The Red Dot Sight and the Reflex Sight can make the HK21 much more accurate for some, removing the bulky rear sights from being used. However, the ACOG Scope and the Infrared Scope do not work well with the HK21, as its moderate recoil becomes a major problem with its reduced centerspeed.
For perks, Tier 2 perks are of most help for the HK21. Warlord can allow a player to use a Red Dot Sight and a Drum Mag for an "Overwatch" class, placing accurate fire without the need to reload frequently. Sleight of Hand Pro can easily mitigate its slow reload and aim times. Finally, Hardened Pro can allow the HK21 to easily rip through surfaces, and flinching won't severely throw off a player's aim.
The HK21 can be found in Zombies mode and can only be obtained from the Mystery Box. It starts with a magazine size of 125 rounds and with an extra 500 rounds. It has a reduced rate of fire from Multiplayer, firing at a measly 535 RPM, making it very unforgiving in this regard. However, the high amount of ammunition at disposal, and the low rate of fire, make reloads few and far in between. That being said, however, reloads can be painfully long, usually tempting the player to buy the expensive Speed Cola. Double Tap Root Beer is extremely useful on this weapon, as the large magazine will still take a long time to deplete, despite the great increase in the rate of fire. However, Double Tap Root Beer is absent on Ascension. The HK21 is often viewed as a "Love it or hate it" style weapon. Some players will love the high magazine size and power; however, others can simply detest the handling of the weapon, particularly the ADS time, reload times, and movement speeds, alongside the extremely slow rate of fire.
When Pack-a-Punched, it becomes the "H115 Oscillator". The magazine capacity is increased to 150 rounds, and the maximum reserve ammunition is increased substantially to 750 rounds, effectively leaving 900 rounds to be used as soon as it's obtained. The damage gets an increase as well. However, the maximum bullet damage of 210 is definitely less forgiving than other weapons, coupled with the excruciatingly low rate of fire; however, the high amount of ammunition offsets this.
In terms of performance, it is often compared to the RPK, due to their extremely large magazine capacities, and LMG statistics. The RPK is generally better when damage is concerned, as the much healthier rate of fire will often prove to down zombies quicker than the HK21 is capable of. However, the HK21 has overall better ammo conservation, and it has a much larger reserve supply. However, both of these weapons have little ammo consumption concerns, barring when the RPK user is using Double Tap Root Beer. Generally, many players will prefer the RPK over the HK21, for the higher damage, in trade for less ammunition, which it packs plenty of.
HK21 vs H115 Oscillator
- The HK21 has a fingerprint on the back of the iron sight.
- The "115" in "H115 Oscillator" is a reference to Element 115.
- Clan Tags are placed on the rear of the iron sights and are completely clear and visible, even when aiming down the iron sights.
- On the Wii version, the handguard and stock are black, whereas the Xbox, PS3, and PC versions have a tan color.
- In early stages, the HK21 had an olive finish rather than a tan one.
- In third person the HK21 has a lot of muzzle flash; however, it is barely noticeable in first person.
- In the Create-A-Class display, the character's arm goes through a corner of the gun's stock.
- The iron sights' range are set to "2".
- In the trailer for Call of the Dead, the HK21 can be seen with a Drum Mag and an Infrared Scope. However, this setup does not appear in the map.
- Despite the HK21's rate of fire being 535 RPM in Zombies mode, Robert McNamara states that it fires "seven hundred rounds", which is close to the multiplayer variant instead.
- When using Double tap, the Weapon will fire at 750 RPM like the Campaign and Multiplayer variants.