In the scope I have had gone bad, generally about 1/4" on a quarter inch click scope. Sometimes they jump and stay for a while and it's these that will drive you crazy. The first scope I had to go bad would jump 1/4", throw a couple of shots there and then jump back to original point of aim. They are easier to pick up on. I have had two scopes go bad on the parallex. One was a front adj and the other a side adj. Now, I generally check my parallex a lot, even if I have to stop during a group because of a condition change, I'll take a peek and see if it's changed. When a parallex goes bad, it will not normally make a big change on target (1/4") but more like 1/8". When a crosshair reticle comes loose, some are easy to catch and some are not. The easy ones are when you look through the scope and it's a X instead of a +.
Hovis
