The SHTF and you call your wife.....
She knows the couple of carbines or rifles to grab, but there are 4 labelled ammo cans to choose from: 1) Fusion MSR .223 62gr, 2) IMI 5.56 77gr Razor, 3) MK318, and 4) the vaunted "FBI Load" 5.56 TBBC.
You instruct her to grab two carbines and one of the ammo cans mentioned above (let's say 600-800rds in each). Which ammo do you tell her to grab? She's meeting you on your way out of the city so you two can seek an appropriate shelter. You *might* be able to come back and grab the rest but which can goes first?