Ruger cylinders are notorious for having undersized, or mismatched cylinder throats. I actually sold my .41 Bisley because of abysmal accuracy... this was before I found out about having the cylinder reamed. I bought a .44SPC Flattop, sent the cylinder off, and the machinist reported that the throats were all over the place, and all undersized. Looking at your photo, it's obvious your cylinder's throats are not all the same, I would recommend having them reamed.
I would be curious as well to see if the copper was stripped off, either in the throats, or after finally making it to the forcing cone.