In this age of black plastic rifles, a stacking swivel (which IS what it is)
seems positively archaic to a lot of the younger generation.
When I did my boot camp rifle range time at Camp Pendleton in 1968, we
spent all morning one day stacking and unstacking our M14s. Who knows
why, because as soon as we got to ITR, we were issued M16s, and
I never laid hands on an M14 again.
Walter