The arm in the original post, a small frame sporting rifle has been identified as:
1)A Remington Rolling Block. All the small frame rolling blocks, No2 and 4, have a flat bottom receiver. The arm in the OP has a hump on the bottom so not a Rem RB.
2) Ballard. The Ballard was made only in a large size frame so not a Ballard.
3) Stevens sure looks like one.