In the config at the top there is a setting Rad, this is the angle of dispersion. The more shells - the greater the angle, to such an extent that at maximum your entire screen is filled with them, as an example - a musket from the screenshots. It is made so that you do not have 200 shells, which together with your one, as if you shoot 1 shell causing 200 times more damage. Experiment with these numbers. If your shells fly to the right, the problem is most likely in the enabled stat that increases the lifetime of the shell. As a last resort, try to simply reset the config to the standard, and if it does not work, this is a problem with the shell itself that cannot be solved, and it is not in the mod settings.