When I got my first Thompson Encore .50 cal , I started out with loose powder, at 90 grains.(Pyrodex select) It took me quite a while to get the right sabots, bullet, powder combination, but I finally got the rifle to shoot clover leaf groups at 100 yards.
Then the pellets came out. I thought they were the greatest thing since sliced bread. No measuring, no muss, no fuss. Then I went to the range. I quickly noticed that the pellets at 100 grains didn't seem to kick my shoulder as hard as the loose powder, and I immediately thought that was great also. But as I shot through the day, I noticed that the difference in the kick to my shoulder, was having a definite effect on my groups. I shot ALL day, and could not get my groups better than 3". I figured I was just having a bad day, and went back home, cleaned up my rifle, and decided to go back the next day and try again.
I did not re-adjust my scope because the rifle was shooting so good, that I did not feel it was necessary.
The next day I went back to the range, and the same thing happened. I could not get my rifle to shoot any better than 3" groups, and some groups would be spread as much as 5".
I then decided to re-clean the rifle at the range, and try the loose powder again. As soon as I put the first three rounds down range, they were touching each other, dead center.
I took the pellets back home, and put each pellet on my scale, and quickly discovered that no two pellets weigh the same. Now I realize that the box says 100 grain EQUIVALENT , but I just could not get comfortable with the idea that every 2 pellets would weigh different. I gave the extra two boxes of the high priced pellets to one of my buddies, and never looked back.
I shoot my loose powder at poker chips at 100 yards, and rarely miss one, and the pellets just won't do that for me.
Just my experience with them.