Summarize the differences between troubleshooting a single-action and a double-action revolver.

I believe this is still going to depend on the make and model of firearm you are working on. For example, with most single action revolvers the cylinder will not move until you quarter or half cock the hammer but with the Ruger Black Hawk single action revolver once the loading gate is opened the cylinder will rotate even though the hammer is all the way forward. On occasion I will get shooters with new Heritage Rough Rider single action revolvers that tell me it will not fire. This falls into the operator error category because often times single and double action revolvers do not have a safety selector, but Heritage Rough Rider single action revolvers have one located on the opposite side of the loading gate that prevents the hammer from coming in contact with the firing pin. On a select few double action revolvers, they have an internal safety that requires a specific key to lock and unlock the hammer. If a customer tells me the revolver is locked up and will not cock or fire this is one of the first things I look for. Sometimes double action revolvers will not allow the cylinder to close and lock and this is usually because the ejector rod has unscrewed to the point where it is too long and prevents the cylinder from closing. I will also have customers asking me how to open the cylinder on a single action revolver to load it. When I explain how to load it through the loading gate they are confused because double action revolvers have the cylinder drop out of the frame to load. This only begins to scratch the surface of the issues customers will ask you to trouble shoot with regards to single and double action revolvers, but these are some of the most common I have come across.