I wouldn't expect it to pattern as well as a pistol. I've heard a longer bbl (more contact with rifling) scatters the shot more so you end up with a very thin donut hole pattern. I notice my shorter bbl pistol patterns a bit better although the difference is neglagible. Have you tried the CCI stuff? I'd give that a try before investing much effort in the DYI. If CCI works ok you can probably do better yourself.
Insanity: doing the same thing over and over again and expecting different results