I don't buy the notion that you should shoot lighter than normal bullets out of a short barrel. Most modern hollowpoints are designed to expand at a wide range of velocities. Also, when you shoot a light bullet out of a short barrel you are significantly decreasing the momentum of the bullet, which may significantly decrease penetration, depending on the bullet design. You also tend to get more muzzle flash from the lighter loads because the powder doesn't have as much time to burn. They also may give you a different point of impact than your standard practice load. I stick with one bullet weight no matter the barrel length.