Marine corps drill and ceremonies manual - Regimental Drum Major ...

(3) As soon as the stackman has placed his rifle in position, both
men move the foot nearest the stackman 18 inches to the oblique
and toward the stackman. The man on the stackman’s left inserts
the muzzle of his rifle into the loop to a point approximately
halfway between the flash suppressor and the front sight. He
holds his weapon in this position until the man on the
stackman’s right inserts the muzzle of his rifle in a similar
manner and above the other rifle (see fig. 7-9).
Figure 7-9.--Insert Rifles Into Stackman’s Sling Loop.
7-11