The Merkel double rifle is on a 20 Ga frame size. Some say they build the double rifle on the 20 Ga shotgun frame, and some say the opposite. But there are different frame sizes. I had a 20 Ga Sauer post war on a 20 Ga frame size. But as far as post war guns go, I really don't like very many of them. The best quality was pre-WW1.