8 inches at 7 yards is terrible. Like, when I took a friend shooting, something he doesn't do often, his first 5 shots were maybe a 6 inch group. Inexperience will do that, but you don't seem to be unfamiliar to shooting.
There could be multiple things at play here. One is the SP101 is not the most accurate revolver ever made and has terrible ergonomics. I have a Rock Island .38 snub that was consistently pulling to the left with the wood grips and I thought it was the crown too, but then I switched to the larger plastic grips and it shot to POA.
But before we condemn the ergos on the SP, as others have suggested, try different ammo. This SP you have may not like wadcutters or it may not like lead bullets at all.
Throat size is important and Ruger seems to love making them big these days. If you have a set of calipers, measure your throats. You could also have a bad alignment of the chamber and bore. You could also have a bad barrel with improper groove/land dimensions.
I would shoot some standard 158 grain LRN and 125 to 130 grain jacketed bullets and see what your results are.