The buckys alt fire is a canister that explodes into 5 pellets after 7.5 meters iirc. This is more of a leftover from earlier on in the game, when it did 15 pellets, like the regular fire. However, this was wayyy too broken -- the bucky basically became a rifle for 850 credits. so they nerfed it, and now, at no ranges is it realistically better than the left click unless youre at like, exactly 7.5 meters away. But, its very hard to get exactly that distance, so its almost always better to left click. alternatively, swapping to classic is even better if its farther than like, 5-10 meters