This is private range that has decided of its own accord to make a particular offer. There's nothing illegal or unethical about that. In fact, they're smart -- they know if more women are at their range, more men are likely to show up, too.
It's not some kind of feminazi conspiracy. Sometimes a cigar really is just a cigar.
Well said. “Ladies’ Day” is a common tradition for various businesses to run, because where the ladies congregate, there the available men will come (and spend money).