Recoil can do it. So can muzzle blast. I cannot be anywhere near a muzzle brake. Having had many concussions recoil/blast headaches are a main priority for me at the range. Calling blast or recoil "concussive" is 100% accurate.
i never understood why someone needs a brake for hunting big game ? even my skinny little adult daughter does not feel the pain when she has shot her husband`s 7 mag. at a deer.
