The same bullet as the "regular" 200gr 45 Colt just .002 larger - the ORIGINAL 45 Colt bullet diameter. Straight walled cartridges, especially the 45 Colt, can have a lot of "blow by" meaning that powder/gases can blow "back" into the receiver and even into the face of the shooter. Many folks try to solve this problem with a heavier bullet - which can get expensive. If you have an older gun with an oversized(?) chamber, the larger diameter may help to seal the chamber when fired thereby reducing blow by.