Replaces some of the weapons' firing (and some reloading) sounds with the (mostly) analogous weapons from Military Conflict: Vietnam. Most sounds are self-explanatory, but there are some oddballs like the HCAR having BAR sounds, and R700 having M40's. Another example would be the M16 having sounds from three MCV weapons, such as the M16 itself, the silenced Mk.4 Mod 0, and the marksman M656 (being the sounds used by the "DMR kit" barrel). These replacements more or less make sense, as they're variations of the same weapon platform.

The MG 42 sound in the video is broken, and some reloads are too quiet, but has since been mostly fixed.
You don't have to install all the soundbanks, you can delete whichever you don't need. Be careful around shared banks, like the AKM/RPK, and the akimbo SMGs. The "GL40" soundbank is shared among most grenade launchers.