Commercial balls and conicals of the wrong size will not shoot well out of anything, that is not rocket science, so I guess your friend may be right as far as stating a fact. Most ROAs mic around .448 to .450 on the grooves and about .442 on the lands I think, at the muzzle. LEE makes a special mold for the ROA, which makes it easier to start a conical in the cylinder. It has a slightly smaller base diameter of .448 - .450 that lets you push the base in with finger pressure, then use the lever for the remainder. I have never shot balls out of mine,I shoot balls only out of my '58 Remi though), but would think you would need something in the neighborhood of at least a .454 or .457 ball to get that shave ring, and still use the "butter". The upper bands on the LEE mold measure at .456. You didn't go wrong with the Ruger by any means. General rule of thumb is if it will fit in the cylinder, it will prolly go out the barrel. Pure lead is pretty conforming to size. I use straight WW and have never had an issue, and it shoots pretty accurate to boot.
HTH,
Okie out