Remember, its the energy that matters when you get hit, not just the FPS.
400fps on 0.2g is 1.48 Joules.
650 fps on 0.2g is 3.9 Joules. Using a 0.43g bb to bring that down to 440fps is still 3.9 Joules.
I wouldn't be anywhere near your friend if he has a rifle shooting anything about 400fps with 0.2g.
And for the love of god, make sure you wear eye protection. NOT safety glasses from some workplace. Proper eye protection.
H&K G36c (KWA) / Glock 18c (TM) / Kimber LAPD SWAT Custom (TM) / Mossberg M500 (ACM)