There are no specific rules for long range air pistol because no one believes that you can use them accurately at 50 yds anyway!
As th HW45 is a springer, I shoot it two handed with elbows rested (but not the gun or your hands) so that the recoil is allowed to occur "naturally". I dont use a backing card for these shots so if I miss I dont know where the shot has gone. When you shoot pistol, the light affects the aim point. Indoor ranges are OK but out doors where I shoot Bright sun or dull sky affects the point of aim considerably. Normally in target shooting the point of aim is below the bull, into the "white" so that you can see the sights. To shoot the playing cards edge on, its best to just have the card without anything behind and aim dead at it. If you dont hit it dead on you just get a slight indentation along the face of the card like a biro line.
I started doing this because I read that it was impossible to cut the card edge on with (any) bullet and it was all a trick because the card would "give" to the bullet. I fasten the card to a post with one staple in the bottom corner so it is free to flex but as you see, it rips. I think the only reason it doesnt go right through is that at 5 ft pds the pellet hasnt got the energy at 50 yds. Incidentally I cant do it every single shot! but the one I did last time (Wed) was on my third shot.