Okay, first things first … if you’re doing kettlebell swings the way I teach them, and you are a healthy, injury-free individual, your lower back should not hurt at all.
On the other hand, there could be some underlying structural/muscle imbalance/etc. issues going on that are causing your lower back pain – regardless of training technique.
My friend Rick Kaselj shot a video special for you – an FVT reader – that covers this topic. He talks about what could be happening, and a few simple drills to fix it. Check it out: