The Commando Carbine (otherwise known as the De Lisle carbine) is acting inconsistently with both its single player version and its multiplayer version. The two main problems are:
1) The weapon causes NPCs in Combined Arms to react as though the weapon is not silent. In the single player, the Commando Carbine does not alert NPCs when fired. This is easily demonstrated by firing the weapon in the vicinity of the NPCs in Combined Arms while out of line of sight. They will immediate become alert and attack the player. Note that this is not related to the second issue of being able to unable to kill NPCs in one hit to the head at close range.*
2) The Commando Carbine cannot one shot kill any NPCs** on any difficulty in Combined Arms, even at close range to the head. This is inconsistent with how the gun deals damage in both single player and multiplayer. In multiplayer, the Commando Carbine will kill enemy players with one shot to the head up to 30m away. In the single player, the Commando Carbine will one hit kill NPCs with a shot to either the head or the chest.
The inconsistency of how the Commando Carbine deals damage in Combined Arms is especially noticeable when compared to other single headshot kill weapons. Perhaps it isn't a priority for it to match its single player damage profile, but it is literally the only weapon capable of killing a player in mutiplayer with a single headshot at close range that doesn't do so in Combined Arms. To be clear, what this means is that the following weapons kill with a single headshot on players in multiplayer and cloth hat / (unarmored) helmet wearing NPCs in Combined Arms:
To reiterate, all these weapons are capable of killing a player with a single headshot at close range. All these weapons are also capable of killing a cloth hat / (unarmored) helmet wearing NPC in Combined Arms with a single headshot. The only outlier here is the Commando Carbine which is capable of killing a player in multiplayer with a single headshot at close range, but is unable to kill a cloth hat / (unarmored) helmet wearing NPC in Combined Arms. This is inconsistent with how all other single headshot kill weapons behave.
Both of the issues can be replicated with 100% accuracy by entering a single player game, Combined Arms game, and a multiplayer game. The Commando Carbine will perform as described in this post.
TL;DR: The Commando Carbine when used in Combined Arms is inconsistent with its single player and multiplayer versions, both in the the damage that it does and that it alerts enemies.
*Tests using throwing knives, when thrown at such a distance as to not one shot the enemy NPCs, show that the NPCs do not need to be killed in one hit to avoid alerting the other NPCs. So long as the NPC is killed before they open fire with the throwing knives the player will remain undetected by other troops in the area.
**The NPCs referred to here are the "standard" ones, identified by wearing a cloth hat or standard helmet. There are armored NPCs which are capable of taking more damage, but those are not the ones referred to here. To see visual examples of the NPCs discussed in this post, please look at this album. Pictures 1-4 show the NPCs with cloth hats and helmets that can be killed with a single shot to the head at close range using the weapons listed above. Pictures 5-10 are the armored "elites" and are not the subject of this post.
April - last edited April
I can see the frustration but CA enemies aren't meant to complety replace human players. Throwing knifes and the Commando have a significantly different dropoff than other Scout weapons (mainly bolt-actions) and shotguns (due to pellet spread and the sniper bullet actimg just like a normal, non supressed sniper). CA enemies also have more health further compounding your problem.
If I remember correctly, the Commando did a pretty good job at picking enemies off while still allowing you to remain unnoticed in sgory mode so it is weird that enemies can auto detect you in this mode (which just happens in Combined Arms for all weapons).
This weapon is a Frankenstein's monster of multiple weapons and I believe it uses modified pistol rounds, not your average rounds