What is a "swamped" barrel?

And I am curious about the caliber. I presume .50 cal is considered sufficient for deer, so is this rifle intended for larger game? Or did the customer simply prefer a larger bore?

I am also wondering if you have made .75 calibers, rifled or not, like the old Brown Bess muskets. And how would their performance compare to .62. Is a lot of range or accuracy lost?