I've seen that posted at a few ranges. As far as I know, it's lead-related but with the number of muzzle brakes I saw (and experienced
) last time I was at a range, I can't imagine the concussive force would be good for an unborn baby. I sat between two guys and their SVT-40s, with foam ear plugs UNDER my electronic muffs. I had a headache for 2 days after. Haven't been back to a range since, but I didn't go much before that either.