The problem with the M1 Carbine, is the bullet. A soft lead, or hollow point round would make the carbine very effective.
When the various threats in the Security Company's areas of operation, are looked at, such as sites that are out in the boonies, or big trucking parking.
A short rifle would be ideal.
The powers that be vetoed that, something like the bullet goes to far?
Having done "Guard duty" at an out door ATM drive through, a short M1 Carbine would be ideal, 15 round magazine, a red dot sight, perfect.
The low recoil would lend itself to accurate follow up shots.