Inaccurate NES Zapper?

I am currently attempting to use my mouse as the Zapper for Mechanized Attack with the Mesen core. I’m not sure if it’s something on my end or an emulation thing or just how this particular game reads input, but the Zapper shots are very inaccurate very often, sometimes with the shot landing on the other side of the screen from where I just clicked and it makes the game a lot more frustrating than it probably has any right to be. Does anyone know what could be causing this?