Warburton Backbore B 3 for Trumpet, Warburtons tightest commercial sounding backbores (1-3). These models have a concentrated and intense sound. The #3 is the most popular of this series. If offers a bright, projecting sound that is great for lead players and outdoor work. The only difference at the B-Series is in the external dimension which is slightly larger and causes a subsequent increase in the GAP.