When Sam and Nicole are approaching the van in the casino parking lot, their guns change back and forth between rifles with carry handle sights and rifles with red dot scopes.
During the firefight at the casino Sam's and DeChamp's weapons switch from H&K 416s with AimPoint red dot sights to standard M4A1s with iron sights.
As they are about to enter the apartment, Kensi and Deeks draw their weapons, Kensi draws from a rear-waist position but when she is viewed from behind no holster is visible. She's wearing tight clothing with her blouse tucked, therefore at least the top of the holster or the belt clip would be visible. Her outfit was inappropriate to the task, as undercover and plain clothes agents need to be able to conceal their weapon, and her outfit was too fitted to enable that.