Just got back from antelope hunting in Wyoming with a pair of Roberts. Steve used an M77 in 257 and I used my old Browning 'bob. Both were pushing 100gr Hornady IL's at 3100fps. Steve shot his goat in the right ham. Bullet broke the big thigh bone went up thru the entrails and broke the back...DRT. I found the flattened jacket when I was peeling out the loin. I shot mine at about 250 yards broadside. I was shooting downhill and hit too high - broke the back. Bullet left a dime size exit hole and screamed off into the sunset.
There really isn't much that you should do with a Roberts that can't be done with a 100gr Hornady...IMHO

“My horn is full and my pouch is stocked with ball and patch. There is a new, sharp flint in my lock and my rifle and I are ready. It is sighted true and my eyes can still aim.”
Kaywoodie