There was another one in Battlefield 1 - an experimental machine gun with two magazines, but only one could be engaged at a time. You would pull one out slightly and push the other one in. The idea was to be able to switch between two different types of ammo for increased versatility (e. g. regular ammo against infantry and incendiary for anti-air). As with most weapons featured in Battlefield 1, I think this was a prototype that never saw any real action.

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Is it a Tesla?

They are transcoding them into the video. Sponsorblock had to make a quick change to discard submissions from users that have been identified to be on this trial system, because it affects the video length, and as such - makes it impossible to have consistent segments