I would say to let the deer come as close as possible and to not shoot a deer at 40 yards, just to shoot it at that distance. I would wait for the time when you need to take that shot, when the deer hangs up at 40 yards. I have been practicing up to 50 yards at a coyote target and shooting great, but I will only try a shot around 40 yards, only if I have to take that long of a shot, but thats me. I say if that is truly what you want to do, got for it. Good luck, let us know how you do!