While most revolvers suited as back-up weapons have similar features, there are a few options to be considered. A five-shot revolver can have a smaller frame and thinner cylinder than a six-shot making it more concealable. There also are exposed hammer, shrouded hammer and "hammerless" or internal hammer revolvers. An exposed hammer can snag on clothing and other items when deployed. These weapons also can snag and fail to fire if fired from inside a jacket pocket or near clothing. The advantage is they can be manually cocked and fired single action for a precision shot.
A shrouded hammer prevents these potential problems but still allows the officer to manually cock the weapon and fire in single-action mode if desired.
Hammerless revolvers are quicker to present as there is nothing to snag on clothing or other items. They also have a lower profile than a shrouded hammer revolver. The only restriction with a hammerless revolver is that it cannot be manually cocked to fire single action.
As for the use of automatics, they also have positive and negative points to consider. On the positive side, they are available in miniaturized versions of most full-size autos. This allows officers to have a back-up weapon that closely resembles their duty weapon. In many cases, these firearms also will be of the same caliber and take the same magazines as a duty weapon. For example, Glock has a full line of duty weapons with matching baby Glocks that fill this role.
One drawback to an automatic is the same feature that makes a revolver preferable. The possibility of "Limp-Wristing" will cause an automatic to malfunction. Additionally, autos are more susceptible to dirt, mud and other factors that can contribute to a malfunction. Therefore, these guns require better maintenance to ensure they operate when needed.
The back-up automatic should have the same or less features as the officer's primary weapon. For example, if the duty weapon has a manual safety, it will not be a big deal if the back-up gun does not. However, if the primary weapon does not have a safety, then the back-up gun absolutely should not have one. If it does, it is likely the user will forget to take the weapon off "safe" because he is trained to operate his primary weapon. This could result in disaster. The functioning issue is important from a practical standpoint. It has been proven in stressful situations an officer will fall back on his training.
Keep in mind the back-up weapon may be called upon to perform the same functions as the duty gun. Therefore, it needs to be of a caliber large enough to provide the necessary ballistic performance. Anything less than a .38 special rated for +P likely will not be enough gun to do the job. While .25 autos, derringers and the like may be good "hide-out" or "Onion Field"* insurance guns, they are not suitable as back-up weapons. However, there are experts who disagree with this. Several semi-autos chambered in .38 auto are popular as back-ups. These weapons are very concealable and have adequate magazine capacity, but still lack in ballistic capability.
Any police supply catalog will have a large selection of holsters for back-up carry. Officers should consider this carefully as their method of carry will dictate how accessible the weapon is when needed. It also will help determine what type and size weapon will work as well with any accessories that may be added.
Vest-mounted holsters. In most cases these holsters allow access to the weapon with either the primary or support-side hand. A vest-mounted holster can be either a holster that rides under the officer's arm secured by the side straps of his vest, or a "BUG-pouch" (BUG is an acronym for back-up gun) mounted on the front of the ballistic vest. These provide a good balance of retention and accessibility. They do add weight and bulk to the front of the vest, however. Whether or not this matters depends on the weapon the officer chooses to carry. Additionally, if an officer is in an all-out fight for his life, with his primary weapon unusable, it may be hard to deploy a gun from inside his shirt.
Inside-the-pocket holsters. These holsters are another popular choice. If used, they are best placed in the front or rear pants pocket on the officer's support side. This allows the officer to access his weapon while grappling and reach it with either his primary or support-side hand. During the winter months, back-up weapons can be carried inside a jacket pocket. This allows the officer to have a gun in hand without anyone knowing it. The biggest drawback to carrying in a pants pocket is it can be uncomfortable when seated. Officers also may need to alter their pants to extend the pocket and make it deeper.