Most ammunition manufacturers define 4 inch and longer barrels as "service" length. GD Short Barrel was specifically designed for 3-3.5 inch semi-auto barrels; the .38 Special 135 grain +P was designed for the 2 inch revolver. If you look at Speer's performance charts, the 9mm standard velocity GD fired from a 4 inch barrel has the exact same energy as the 9mm +P Short Barrel ammunition fired from a 3 inch barrel.