I bought the 3.5-10x40 off fleabay.
Put it on my BRNO and the best I could get was a 5" group at 25 yards
The grouping started bottom right and finished top left in a diagonal
For the price I payed for it I thought it worth taking apart. Getting the eye bell off was a job in itself (babyboa job), low and behold in the eye bell was another ring that had come off the main body of the scope..... I chucked it away, put the eye bell back on after checking the glass with the ret etched on it was solid.
When I finally got to give it a test I was getting 1 hole groups a 25 yards
Apart from that problem, I only had to re-parralax it to the markings on the side wheel.