Come to think of,it did have a slight hump
Like this one?
- pic from
http://ugca.org/03mar/savage.htm
That's a later version of the 520 (the 520-30), in WW2 trench gun garb, the older ones actually had a double hump like the receiver of a BAR. And there's a picture of a 620 just below the pic of the 520 at the ugca link.
They were also sold as 'store brand' guns by Montgomery Ward...