Different theory on pattterns
 

It's my opinion that hot powders jar the pellets, distort them, and cause blown patterns. I think the shell companies like hot loads because the shooter's shoulder tells him "This is a powerful SOB"

When I was shooting pheasants in Springer trials the object was to shoot the bird as far away as consistently possible so we could if the dog could mark and retrieve.

I worked up a load of 26 1/2 gr of 800X and 1 1/4 oz of #6 shot. 800X was the slowest stuff I coud find. It worked well enough I kept getting invited to shoot more trials.

I tried buffering the pellets with Grex, but didn't see any improvement

Your object to shoot pheasants as far away as possible doesn't agree with my experience. At a Springer trial where I was gunning, I missed a pheasant with my first barrel, picked him up at about forty five yards at the edge of a woodline. The dog must have belonged to one of the bosses, because I was not invited back. It was the only shot I missed all day.