Free Traders have a difficult time of it. Between difficult locals, pirates, crazed passengers, and hijackers they need weapons to be as easy on their ships as possible.
This is compounded by passengers. Sometimes an emotional disturbed passenger (or even crew) will pose a danger to the ship or themselves. Stunners are usually cutting edge technology well above what most merchants encounter let alone support.
Enter the trader carbine.
Trader carbines are unspectacular weapons at first glance. They are almost never equipped with slings but almost universally have folding stocks. Their beauty lies in their ammunition. Rounds and clips are color coded, green, red and black.
Green clips hold tranquilizer rounds similar to those fired by snub pistol though not low recoil ammunition. These rounds are used to take down an emotionally disturbed or incoherent passenger or crew.
Red clips hold squash heads. These fire special rounds that are conical when fired but assume a spherical shape after hitting an armored body or wall. The spherical shape sheds velocity fast so they are less likely to penetrate a partition or control panel after striking a target. This round is used to repel boarders on your own ship, when you'd like things to remain functional afterwards.
Black clips hold armor piercing rounds. Penetration is essential when fighting opponents in spacesuits. The rounds remain effective against unarmored targets. They're used outside the ship or on another person's ship. Sometimes a boarding action goes awry and traders will turn the tables on pirates. In many cases they try to inflict as much damage as possible to let them make a quick getaway.
As a final safety measure many carbines are equipped with a recognition system to read the user's thumbprint and not allow an unauthorized user to fire it. Cheaper alternatives are a kill switch triggered from the bridge and a hidden safety, a small innocuous protrusion that can keep a stolen carbine from firing.
Many merchants carry supplies and fabricators capable of turning out ammunition for their carbines. In fact the trader carbine (in a modified form) is a prime item for trade. The modified carbines will only fire green or red rounds.
Trade carbines use the range modifiers for the carbine. Green rounds use the rules and armor modifiers for snub pistol tranq, black rounds use the armor modifiers for snub pistol HEAP. Red rounds initially function as normal carbine rounds but have much less penetrating power after hitting a target (if you're checking for bullets passing through a body or ricocheting the red rounds have a 4 in 6 chance of petering out or being stopped dead.) Ammo cost for tranq or HEAP rounds are doubled.
Carbines still hit as a shotgun. Tranq rounds do 3d to endurance only and damage does not affect other characteristics. Red rounds do 2d damage(or 1d for ricochets). Black rounds do the normal 3d damage.
Trader carbine ammunition is not usable in other weapons (even normal carbines).
Finding a kill switch on a trade carbine is a Difficult Task in CE (10+ in CT) modified by INT and Mech skill. Kill switches cost 100 cr. and must be installed at time of purchase.