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Carmine is correct. Suppression is dealt on a per bullet basis. However, one thing he does get wrong is the maxim's suppression, the maxim actually has worse suppression per bullet then the MG42. I dont know the exact amount required to suppress a squad but that isn't really relevant for the following numbers.
The maxim has a long range rate of fire of 7.2 shots per second and deals 0.0065 suppression per bullet for a total of 0.0468 suppression per second.
The vickers has a long range rate of fire of 14.4 shots per second and deals 0.00805 suppression per bullet for a total of 0.11592 suppression per second.
The MG42 has a long range rate of fire of 14.4 shots per second and deals 0.012 suppression per bullet for a total of 0.1728 suppression per second.
The Mg42 has 300% more suppression per second then the maxim and 50% more than suppression of vickers. The only advantage the maxim has is that its bursts last about 175% longer at long range which lets them fire more bullets before needing to cooldown. This however does not compensate for the lack of suppression per bullet and low rate of fire.