You start with Computer/1 on the gun. You turn it into a specialised computer, which basically makes it Computer/3 but you can't change the programs built into it.
You then give it Intellect/1 and Expert/2. It doesn't need Intelligent Interface because the user isn't using the Expert program - the Intellect program is. The gun now automatically adjusts its targeting system, recoil etc to maximise the user's chance to hit.
Coming very late to this, but the thing I don't understand is that Expert programs can only work for INT and EDU based skills. gun combat uses dex. I don't really understand how an expert programmed gun helps at all.
I could imagine Expert Recon or Expert Tactics, tied into the gunsight and 'tagging' high priority/concealed threats.
Alternatively, Intelligent Interface allows you to use a weapon with a shot selector and multiple ammunition types - as per a rather famous handgun.
Alternatively, Security provides a bit of reinforcement to Secure Weapon - preventing someone who's acquired the weapon from defeating or bypassing the security system with agent software or cunning rewiring.