I dont feel a bit guilty at shooting at 20 yrds. This is actually a litle farther than I would like. 15 yrs is a grand slam, but as you go out to 30 and 40 you are adding a grouping of 3-4 inches and its hard to put it in the boiler room at that distance, especially when you cant get the deer to posture so you you can get in behind the shoulder.
Wory about the 20's and 25's even 30's but dont even try to take a shot unless he is broad side and has a Sharpie with a circle drawn on his vitals.
Get a blind and como it, get in a tree, and you will find that your shots are less than 20 yrds.