I don't use Konstantin that much either, however, I have put enough time into every character to sorta know what works best on them. Konstantin's weapons (like most of the other raiders) depend on the players playstyle.
His base gun is good but boring and I don't recommend it compared to his other guns. His second common shtorm, or however its spelled, is way better in every aspect but is basically the same with a piercing gimmick; If enemies are in a row you will damage the whole row. Tolchok is an amazing gun if you want to keep a distance between you and the enemies, however, with the recent update to push effects idk how if its still a viable option.
His rare guns are quite interesting as well. The UV9 can shoot a rocket if kept in the middle pressure however it is not instant and you cannot shoot while the rocket is charging...a good gun but I don't use it myself. His hornet is an amazing gun and my most used weapon in his kit. Basically its like his base gun but WAY more accurate. It is basically a death laser that has bullets that bounce off cover, floors, and the roof. Think of Ginebra's rare gun but in a more direct fashion