When creating the holster we did so with three particular criteria in mind. For safety, ensuring the trigger inaccessible when holstered. For speed, ensuring the grip is adequately accessible for retrieval.  For usability, when worn while seating or conducting usual daily activities the holster remains comfortable.  

We also chose to use law enforcement rankings instead of traditional sizing, such as small, medium, and large.  We found that when we used traditional sizing methods there was a lot of opinion over gun sizes and which qualified as what size.  By creating a ranking system we helped to alleviate the issue.    

Our holster sizes are designed around specific firearms ensuring a proper fit and smooth draw.  We do say the holsters are more size specific then firearm specific though.  The reason we say that is often one size holster will fit many firearms.  For example, our Lieutenant holster fits many the Shield (9mm and .40), XDs 3.3, Sig 938, Glock 26/27 and 43, a Ruger LC9 and even a 2” revolver, among others.  Typically, a Cadet fits most Pocket Pistols, a Trooper fits most .380s, a Lieutenant fits most Sub-Compacts, the Captain most Compacts and the Colonel fits most full-frames.  While this is a generalization and we want to ensure the proper fit for the specific firearm this also allows the carrier to use the same holster for several firearms, and the 5 sizes allow coverage of thousands of guns.