LM: The Class III stuff is in the same high-security case as a doctor's bag full of DEA restricted narcotics. He's more worried about losing the narcotics than the FA weapon as a doctor, since if he loses narcotics due to his negligence, he can lose his license.
Trust me, the case is secure. He's also got a P-14 pistol where he can get it - the M-4 and the grenade launcher is in case he REALLY needs it.
George has already trained Sam and Ralph in how to use military weapons as part of their training, Just having the M-203 is worth 20 years per round, so the M-4 isn't much of a extra charge!
The whole case is designed for situations that the P-14's can't get them out of - then you'll want as much firepower as you can muster, even if it's illegal!
Fleataxi