For the past 5 years I have used Mobile 1 20W-50 synthetic oil for my personal weapons, as well as used it on two deployments to Afghanistan. I have used it on all my personal weapons as well as my issued M4, M9, M249, M240B, M2, as well as a one time use on a MK19. It doesnt run like CLP and doesnt evaporate in the 130 degree temperatures.
Its against reg, but it did better than what I was issued.
Never mistake Kindness for Weakness