Dave - I have the Tasco 20x42 SS scope. I put it on my 338 RUM until I could buy a Leupold Mk IV. This scope is the same as the 10x42 except it is twenty power. There are several reasons not to use this scope for LR use.
1. The biggest problem that I have with mine is that it's adjustments are not repeatable. Many times during the same shooting session I would put X amount of comeups into it and the bullet impact would not be where anticipated. Even going back to the same target that was sucessfully engaged before, the comeups would be different the next time. No confidence in this type of system. 2. It would not always come back to zero everytime. It would be close to several moa's out. Not good! 3. Too little eye relief! I would always be hit by the scope when it was on my 338 RUM. 4. The reticle has visible debris in the field of view. 5. The clarity is lower than every other scope that I currently own. Several steps below my Mark IV or a Nightforce.
They are affordable scopes for sure but to use them for serious hunting or target shooting they fall short of expectations. My Mark IV is worth every penny of the thousand dollars I spent on it. I think there is a lot of hipe about these Tasco scopes from the people that are selling them down in Texas.
Save your money and buy a Leupold or a Nightforce. You will be $300 ahead from the start.