At about the 30 min mark, as the Marines are landing on the beach you see a few Marines firing .30 cal machine guns mounted on the Amtraks At one point you see a gunner pull the cocking handle of his weapon - in the shot the cocking handle is on the left side of the weapon. Likely the shot has been reversed as a .30 cal with the handle on the left simply never existed.
Msgt is correctly referred to a "Gunny." A Marine Gunnery Sergeant has three stripes above, and two below, which is the insignia of Msgt Basilone.
Throughout the mini series Elmo Haney was referred to as "Gunny" However the rank insignia on his uniform was that of a Staff Sergeant.