I don't think a scope will help much....
.it sat in someone's closet for a bit over a million years...they went to move, found it, gave it to someone else...they had it for about a million and a half years...they forgot they had it...I ended up with it...
I've got a cheapie scope, also from Walmart, that I put on an old shot-out remington .22 pump that key-holed at 25 yards. I took the scope off when I got a $100 bucks for the gun at one of Mayor Daleys/Fr. Pfleger's gun "buybacks".
I put the scope on a Marlin 60. If I do my job, it makes nice tight groups.
Sounds to me like the problem is with the rifle, (or mayhaps the shooter

), any scope should work, since there's little to no recoil.