Changing Leads vs. Chokes
I’ve heard people talk about changing their leads instead of changing their chokes. Which has the most effect on the size of the shot cloud?
This answer is probably going to ignite quite a few already-too-short fuses, but you asked for it!
I defy anyone to show me how changing shot sizes can change the size of the shot cloud greater or more precisely than changing choke! In my experience, it just won't happen. That is why I shoot an over/under shotgun: to take advantage of having two chokes. The reason you change choke is to give you the largest diameter shot cloud at the distance you are going to break the target.
Maybe it's best to explain this using a specific example.
Let's say that you are shooting a report pair of crossers. The first bird crosses at 15 yards and the second crosses at 30 yards. If you shot a semi-auto, I would recommend you use an improved cylinder choke with 9s on the close bird and 8s or 7&1/2s on the far bird. There will be a difference in the diameter of the shot cloud at 15 yards using 9s instead of 8s or 7&1/2s, but it will not be very much!
The ideal choke and load for this pair would be cylinder or diffusion choke with 9s on the close bird and improved cylinder with 8s on the far bird. Cylinder or diffusion choke will yield a 22-28 diameter pattern at 15 yards with 9s, depending on altitude, humidity, and your individual gun and load. Improved cylinder, on the other hand, will yield a 14-18 diameter pattern at 15 yards given the same variables. At 30 yards, improved cylinder will yield a beautiful 28-30 pattern using 8s.
The larger diameter of the shot cloud, the greater the pointing error you can have and still break the target!
My advice to you is to change choke if you want to achieve the greatest and most consistent effect on the diameter of the shot cloud!