say ya find a repeating-rifle grenade launcher...would it use plain grenades only or other types like nuka quantum grenades etc? gotta maximize firepower! would think there would be some kind of teargas rounds as well. EMP might work on bots and other machines...

Yeah it is. Every weapon that fires some sort of rounds has different types of them. And if it doesn't....
MODS

I'm pretty sure every bullet calibre has a craftable ammo type, like incendiary or armour piercing or fragmenting. Things like EMPs might be a craftable explosive or a different ammo for the grenade machine gun. But alternative ammo types have drawbacks too, so fragmenting bullets would have more effect on exposed areas (eg. hands and heads (without a helment)) but does not pierce armour with the efficiency of normal rounds. Incendiary rounds might have more effect on insects or such the like, but less effect on people. An EMP may be an insta-kill to a robot but have no effect on an organic creature, though probably not that extreme.

yea remember most of that stuff from FO tactics BOS...