Bob makes it look easy. Believe me it isn't. Judging the wind is difficult and typically you only get a shot or two before the pigeons figure out it's time to head to safer pastures. (or silo's) If you can get them to hang around a while as you get zeroed in it's not too difficult inside 100 but the challenge at least for me is to make the first couple shots count. You need to be out of sight and the gun needs to be as quiet as possible.
POI change when shooting at steep angles the wind and cold weather doesn't help. Needless to say you need a finely tuned gun and as solid a rest as you can get. Accuracy goes without saying and SKILL
I've been working at this and I'm trying but haven't achieved anything close what Bob's doing. It's a journey.
Good luck in your travel's Bob. Be safe.