After making some fine adjustment to the scope I decided for the fun of it to check the trajectory. I set the target initially at 15 yards, firing one shot with the same POA ( fired two @ 20 and even with the scope set at 10x I had a hard time telling the hole was from two pellets) I then moved 5 yds at a time out to 40. I ended up with a 0.5" group. So for most airarms quarry there is no hold under/over from 10-45 yds.
My last group of the day was at 65yds and measured 1.25".
None of my shooting was from a bench, I was standing leaning on top of my car. I have a bench rest but was too lazy to get the chair and rests out but will next time.
BTW, The S400 Classic is in .22 cal and I am using the inexpensive Tasco Varmint 2.5-10X42 with Mil-Dot in Millett AG rings.