That Targetmaster is a great deal at $110 unless it's just completely wasted. It's a well made, accurate, full sized rifle. It's going to be hard to beat. A piece of advice a friend gave me a long time ago was, "I might by a $100 used rifle, but I wouldn't buy a $100 new rifle." Handle that 510 and compare it to a new one you can get for the same price, then make a decision.
The 550-1 gets a lot of love by its owners, but I don't have any first hand experience. RFC has as much info as you could ever want on them.
RT
**edit**
If that is the Model 41 Targetmaster, I don't have any first hand knowledge, but the same rules probably apply.