The stuff from Hard Targets (as well as Run & Gun) adds on to the stuff from Core.
So, your heavy pistol could have a suppressor on the barrel, an infrared flashlight for low-light-vision people, an internal smartgun system, and have room underneath/on the sides.
Or, if you're using a Guardian (which, to the best of my recollection, can Burst Fire but only as a long burst), you can certainly give it a barrel-mounted gas vent, a collapsible stock, and maybe a scope on top. Maybe an extended clip as well, if you want a long-range, high rate-of-fire handgun.