I believe the little plastic cup is intended to keep odds and ends accounted for when doing maintenance. Which is very odd, since no part of the gun save the locking block will fit in that 'lil cup. I use mine as a thumbtack holder on my desk.
My dad carried a Beretta 96 as a cop for about ten years, and he was amazed when he could do much more rapid followup shots with a gun about 1/3 lighter.
Beretta PX4 Type F Fullsize .40 S&W | Beretta 92FS 9x19 Para | Beretta 8040 Cougar Type G .40 S&W | Rock Island Armory GI 1911 .45 ACP | Sig Sauer SP2022 Stainless 9x19 Para | Sig Sauer P6 9x19 Para | Colt Python 4" .357 Magnum | Colt 1968 Det. Spec. .38 Spc. | Ruger LCP .380 ACP | Daniel Defense M4V1 5.56x45 | Alpine M1 Carbine .30 | Steyr M1895 8x56 | Ruger 10/22 .22LR |1943 Izhevsk Mosin-Nagant M91/30 7.62x54R | Remington 870 12GA