When you begin testing it is essential to gather data on volocity of the rounds chosen to use for self defense and practice. This information assists with understanding what your round may or may not do depending on distance to target, whether the target is bare skin/hide or protected in some form. It will also allow you to better understand ballistic preformance when encountering barriers such as standard mobile home walls or brick and everything in between.
This site allows the individual interested in self defense but not financially able to invest in extended testing utilizing chronographs, gelatin and more to gauge velocities. Additional information can be found via several great gel test sites available. Remember, every single firearm regardless its mass production beginnings is different in some form. It could be a simple burr or variation in rifling that allows a minute but discernable difference in both handling and capability.
However, for the average shooter, none of this matters. Though testing a minimum of 250 of your chosen self defense load should always be completed prior to settling on one.
Remember, test everything, have backups and always be prepared.
Free the mind and the body will follow