I fired my new M4 for the first time today. 75 shells of the 2 3/4" Federal LE full power buckshot variety. The lady from Benelli's tech support line said to use full power loads to break in the new springs. I took 125 shells with me but got rained out b4 I could shoot 'em all. To be honest, my shoulder was hurting after 10 shells.
ARGO, shmargo, my M4 kicks like a Minnesota mule !!
That being said, inside of about 50 yards it's my go to gun now. 50 to 200 yards LE 6920, beyond that it's M1A time.