From: Phoenix, AZ
Keep in mind, MGs are most effective against fast moving and "ready" troops. "Ready" in this case means, "ready to get mowed down like wheat." After the first burst, the squad will be pinned, which means the unit is down and, presumably, seeking cover.
Your first burst from an MG will do the most damage. Anything else just adds to the suppression and doesn't necessarily get you more kills.
If you are referring to the squad's MG, then the shots from the rifles will get the unit pinned, thereby also reducing the effectiveness of the squad MG.
You could do a test (if you are so inclined):
Buy a bunch of Russian infantry. Set them up so they have to run across open ground and then use various MGs to cut them down. You will see the effectiveness clearly this way.
Everyone is a potential [PBEM] enemy, every place a potential [PBEM] battlefield. --Zensunni Wisdom