I love #4 shot. I know it does'nt carry the number of pellets downrange, but I love the energy delivered at the point of impact.
For the record Clark, I still use # 4 shot for gobblers for the downrange energy. I'm curious why anyone would want shot smaller than # 6's as well...
If you are speaking of #4 lead, I must say that I am not a fan of it for turkeys. And contrary to popular belief, larger shot size does not mean more downrange energy. Heavier-than-lead has totally changed the old way of thinking in regards to #4 vs. #6 etc.
For example, #4 lead does not actually have as much downrange penetration energy as #6 Hevi shot or #9 TSS shot. Density is a new player in the game, and is a very important consideration in deciding what size shot to use today.
I did a comparison of #4 lead's downrange penetration energy (40 yds) compared to 18g/cc #9's. I wanted a medium that would be resistant to penetration, and came up with steel/tin roofing sheet metal as an acceptable and fairly convenient one to use. I shot various turkey loads at the sheet metal at a measured 40 yards, through the same gun.
Here are the pictures of the results below. In these pictures, you not only see the penetration of each pellet, but you also get a good look at the differences in pattern densities between the different loads. The results explain why I shoot #9 18g/cc shot instead of #4 lead at turkeys.
Federal Premium Magnum 3" High Velocity 1-7/8 oz. copper plated lead #4s
18g/cc #9's (handloads) at ~1100 fps
2 oz. of #6 Hevi-13 does at 1090 fps
There are just so many loads available these days that perform so much better than what was available 20 years ago.
What would cause you to use or consider using a shot size smaller than #6 shot?
So, to answer Clark's question, denser patterns and more per pellet penetration energy are the two reasons I use smaller than #6s.