Mauser = Mowser. I wasn't aware there was any other way folks pronounced it. If they are saying it some other way, they're saying it wrong. Just like (in German), braun = brown, not brawn. But, if there's an umlaut (the 2 little dots) on the a in au, it gets said like the German "eu," which in English is the "oi" sound. This is why you'll hear people pronounce bauer as boyer, Neumann as Noyman, and so on. In North America, these surnames almost always lost the punctuation and the pronunciations got "Americanized." Many of us who are descendants of German ancestors, just gave up on correcting people, and accepted these new names.
Who knew a CGN rifle forum would turn into a lesson in European phonics?