I think you gave up on the first rifle to soon. Even though I own a Z5 and it seems to be a great rifle Winchester does not loan it's good name to crap so you probabally had a fine rifle to begin with.

You never gave the rifle a chance and expected it to behave the same at 60yds as it does at 100yds with only from what I can glean from this thread one box of bullets. The gun isn't even broken in at this point, preferred cleaning methodes developed or anything.

Good luck with the Omega but be prepaired for the same results till you have it tuned in.