UTG Scope headaches

Scope Problem. Hi - I recently bought a RWS 350 Mag .22 with a UTG 4-16 illuminated scope. It was stunningly accurate when it arrived, but is now giving me fits. I keep re-zeroing at full magnification and 45 yards. I typically get .5" to 1" groups. Then, I zoom down to low power, re-focus the parallax, shoot at (and usually miss a starling), and zoom back in to 45 yards at full magnification. Sometimes it is close to zero, but others it is as much as 6 inches off in any direction. Rings and all mounting screws are tight. I need a scope I can count on - is this a common problem with the UTG? (It is my first UTG) - I don't care nearly as much about the money spent on the scope as all the time and effort I am wasting on the process - and frustration over all the missed pest birds! What scope would you recommend that I switch to? Randy PS - I am a very experienced shooter, I can get 1" groups at 500 yards with my high-end hunting rifles. I am shooting the pellet rifle off of sand bags and completely floating it when aiming at targets. When I am missing birds, I am usually on a trigger stick tripod and my shoulder....
 
Usually UTG scopes should not behave like this. 6 inches difference is too much. Could be that the springs inside the erector tube are moving around freely. Did you over turn the elevation or Windage knobs to the extreme end? That could have caused the spring inside to free up thereby causing such a difference. Other reasons could be that your gun is clipping pellets. Try removing the shroud and shooting if you gun has a shroud. Else borrow another scope and try it on your gun. If that works then at least you know that the scope indeed is the real problem. Also check if your mounts are aligned. 
 
Not trying to kick up dirt . But it's just my humble opinion that Leapers and UTG scopes are not very well made . I've owned a couple ( won one in a contest ) and I've owned my last one . Both had issues , AO wouldn't adjust on one , along with mag adjustment being insanely hard to move .
The other looked like the glass came out of an old syrup pitcher . I'm like most and have brands I have had good luck with , but I'm not a fanboy about any of them . I know a lotta guys swear by UTG but to me I've learned my lesson . I hope you can get it worked out .