From Halopedia, the Halo wiki
The MA5K is a cut-down version of the standard MA5B assault rifle. It is fully automatic and receives a thirty-round magazine of 7.62×51mm FMJ-AP ammunition. The most conspicuous difference between the MA5K and other MA5 models is the replacement of the distinctive electronics housing with a removable carrying handle similar to that of the BR55 battle rifle. The handle probably integrates a digital ammunition counter like the BR55 and other MA5 models.
The 'K' in this weapon's designation follows the tradition of 20th and 21st German weapons including the letter in their designations. 'K' stands for kurz, German for short.
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