The guy runs a business and has the right (not politically speaking) to refuse service to anyone. Who cares if he restricts muslims from coming to his gun range, he makes a living obviously and doesn't need their money. But, to keep them out he could go to the local butcher and ask of some pig's blood the next time they slaughter pork. Then he could "christen" the area with pig's blood and let it be known and then they wouldn't come...
My understanding is that if that happens they are not supposed to come if that is the case.