As the Experimental Grg m/49 loads 2 shells it needs the option to load 2 different shells at the same time as long as its available in the characters inventory, for example your first shell can be either smoke or EMP and the second can be any shell that causes damage. As I find that the shells that does no damage are pointless in single player as by the time the player switches between the ammo types the EMP or smoke effect as worn off. Also when doing this it needs a slight delay between 1st and 2nd shell being fired to allow the 1st shell to have an affect on the machines.
Back when I used the rocket launcher I would take both, a level 5 and level 6 launcher. I would load the level 5 with an EMP round and the level 6 with twin explosives. Stun then blasted the machines.
BYW, the second round does not aways follow the first round and sometimes misses altogether and iffy if it does anymore damage than a single round.
But I also would stealth around an area and place field radios so I could attack, fast travel away before the machines go into combat mode. Wait a few minutes while I reloaded and fast travel back to a different radio and attack from a different angle. I attacked harvesters mostly this way and it would lure the hunters away from the harvester. This was fun in solo play but I now like to use the RPG with scope and dual view attachment.