To get the correct holster model fit, you need to know the barrel length of your gun. It’s important to know that even on the same compact handgun, such as the M&P 2.0 9mm, it’s possible to have a couple of different barrel lengths. One reason to check the barrel length is that some holsters have closed bottoms, and if the length of the barrel is not measured correctly it won’t fit the holster.
Pistol Barrel Length
Pistol barrel length is measured from the back portion of the ejection port to the end of the barrel. Gun barrel lengths are measured in Imperial standard.
Revolver Barrel Length
Revolver barrel length is measured from the face of the cylinder to the end of the barrel. Most modern revolver barrels have lugs beneath the barrels. This is an extension that may run the length of the barrel that encloses the ejection rod. Check your model designation at the manufacturer’s website if you have questions about the length of your gun’s barrel or barrel lug as both can affect holster fit. Gun barrel lengths are measured in Imperial standard.