Well, if magazine capacity is the ruling choice, there's the calico 950. Comes with 50 and 100 round magazines.
There was one semi auto handgun that had a 20 round mag in 9mm. I forget what it was called, but it was ugly as all get out,was rather heavy, and the trigger pull was so bad it took both hands holding the gun and one finger from each hand to even get the thing to go bang. A fellow had one at the range several years ago, and he allowed me to try and shot it. As tough as it was to pull the trigger, it would have been a miracle to use that POS in a survival situation and survive. What really hurt is it was also quite pricey. The trigger pull made even our current lawyer proof triggers seem well adjusted.
Paul B.