M142 craddle question for the M60

[har1690]

I have one of the following M142 craddle (M142 cradle mount for M60 machine gun desert tan color - Other Gun Accessories & Parts at GunBroker.com : 939456002 ) and while I understand where the .30 cal ammo can goes, to me it just does not seem necessary that once the ammo can is installed that the other spring loaded "flapper" is needed. Seems the ammo can is in well enough and the spring loaded part doesn't really hold the can from falling out or connects to anything, maybe while installed on a HOMVEE going over a bump...