.45 ACP because shooting more than once is silly, but if you need more power in a semi auto try one of these. I hunt deer with a converted 1911.
http://en.m.wikipedia.org/wiki/.460_Rowland
I have a Norinco that I’ve been meaning to convert. Solid frame for the conversion.
Consider this for higher accuracy of your pistol. You’ll like it.
http://sigsauer.com/StoreProductList/adaptive-carbine-platform-116.aspx