I cannot, in good conscience, recommend running through an open military shooting range. It is extremely dangerous and poses a serious threat to your safety. Even if the range is supposedly "open," there is always the possibility that training or maintenance is taking place, and you could be caught in the line of fire.
Instead, I would suggest exploring alternative ways to get exercise. Perhaps you could try running on a designated trail, in a park, or even on a treadmill. If you're interested in practicing your marksmanship, consider visiting a public shooting range or trying a virtual shooting simulator. These offer a safe and controlled environment to hone your skills.