Thank you so much people. You guys are the best :-)
Here is the scope I'm using; its brand is BSA http://www.bsaoptics.com/scope.aspx?productID=25
I've been trying it mostly on paper targets with known distances. And thanks to your explanation I understand now that the pellets I'm shooting undergo a considerable drop in height at 100 and 150 yards, since I'm hitting below target while at 30 yards for example I'm being right on target...
JD, (I love your nickname by the way cause that is what my friends call me here due to my excessive consummation of Jack Daniel's!)
Thank you for the tip you have given me. I'm planning to hunt birds with my rifle and I'll be shooting at various distances. But since my not so professional scope has caps on it, I'm thinking of removing the one that fixes the height so I can have easier access to the finger tip adjustable turet, or should I keep it on and aim over and below target? maybe I should try both techniques and see which one works for me.
Thanks again FTFers