Red dot fills more space in the big case and will be less position sensitive than bullseye due to that fact. It's also much easier to let an overcharge slip by with the bullseye, but since attention to detail is key that really shouldn't be a problem. Bullseye is a faster powder also, but there are exceptions where this is reversed. I would personally much rather use red dot in the big forty five case. You should actually be able to find plenty more loads for the colt with red dot than bullseye whether up to date or not the data is still use able.