I found that if I used shot cups, I could stretch the effective range out to 35 to 40 yds. The cups I bought come without any cuts in the side walls. You can conform them to your needs. I found that if I cut the walls in three places down the sides about 3/4 of the way, this works great for me. I only use a wad over the shot. I also used 85 grs. FF Goex.
I also have a TC side lock, New Englander. Love it.