I just got a Gehmann 590 compact receiver sight in and mounted it on my Sport, along with a Gehmann 510 adjustable iris with a 30mm extension tube. The gun had previously been zeroed with the factory irons, and when I got the Gehmann units they all lined up with those factory irons. Tried a quick bit of shooting, first at a soda can at 10 meters, good hit, then some swingers on a dueling tree at same distance. Then I tried some swingers out at about 50 yards. Three side by side, ones on outside a square with bottom inside corner cut off to allow for a smaller diamond shaped one to hang between them. First shot at the diamond hit the left swinger, as did the next couple of shots, so I gave the sight a couple of up clicks and some to the right and then it was a go. Had a soda can there also and bouncing it around was easy.
The gun is rather hard to cock if I try to just push the barrel down or tap it with my hand but I did find a way to cock it easily, I was shooting from a patio chair one leg crossed, left elbow on leg for support for hand on forearm. I simply held barrel near the muzzle with left hand, right hand on pistol grip and tapped the end of the forearm on my leg and it unlocks easliy.