I'm waiting for someone to explain to me how the skills needed to operate a pistol and a rifle are so different as to warrant separate specializations.
Whereas, in Engineering the specializations are hugely different. Power plant, Electronics, Maneuver Drive and Jump Drive. Power plant, for example, I assume would cover fusion plants, fission plants, solar power collectors, internal combustion and batteries, to name a few.
With this same logic Slug Weapons under Gun Combat should include all rifles, pistols, SMGs, shotguns, assault rifles etc. that fire slugs using the same mechanism.
Laser Weapons should include all weapons (pistols, rifles, etc) that include the same systems as well.
What you're almost inferring here is the introduction of SUB-SPECIALIZATIONS, something this game system and its character generation couldn't encompass.
Players trying to overspecialize in Gun Combat would be defeated, first of all by a great game system and character generation system, that like real life, often leads to characters very different from the life path they intended. Secondly, I like players that try to over specialize in combat skills and leave themselves so disparate in every other area, like piloting or comms. One situation in which the player finds his character the only person left to fly the landing craft and dying in the crash because of the -3 untrained die modifier, and he'll be sure to spread his skill points around more liberally next time (in spite of my warnings, this actually happened BTW).