The Mk 108

Mk 108 - that designation stems from "Maschinenkanone 108". The figrue has no special meaning. All items developed for the German aviation ministry received a numerical code, and few figures were re-used. Mk meant Maschinenkanone, MG meant Maschinengewehr and otherwise the letters in front of the figures were usually telling about the company or lead designer (similar as with the Japanese navy: A6M = naval fighter, sixth, Mitsubishi).

Most of the sounds in these videos are fake, for gunc ameras had no audio recording. Only a handful of dedicated recordings for propaganda and training purposes may have had audio recording, but I doubt it.

Concerning the Mk 108 in War Thunder:

Its shell is very, very slow and low density. You need to lead aim much farther forward of the target than with 13 or 20 mm guns, and this is important to know since all Mk 108 users but the Me 262 series have mixed armament.

The lead target indicator in AB mode will always be for the biggest calibre that's ready to fire. In a mixed 30 mm + 13 mm armament, it will be for 30 mm. In mixed 30 mm and 20 mm armament it will be for 30 mm, period. The other guns need less lead in deflection shooting, which means that with mixed armaments you better do not aim far forward (such as at the pilot of aB-17) with the Mk 108, but instead a little less forward than you otherwise would. This gives your other guns a better chance to hit at least the tail. This matters the most against the short fighters, obviously.

Even better, hold back your 30 mm fire until at about 500 m, and then one long burst for the kill, break.

You won't need the 30 mm gun pos on the Bf 109 G-6/-10/-14 to kill if you can aim well. They're awfully heavy anyway. It sure is delightful to see just about every target disintegrate in a huge explosion after but a short burst, but a single gun really is much better for survival.

Remember that a low muzzle velocity weapon such as the Mk 108 requires that you aim rather high at long ranges, such as in head-on engagements (which you really should avoid if possible) or generally at ranges 600-1,200 m. I don't think more than 800 m is practical with Mk 108 even in AB.