aFunctional dummies without shot are just that - inert shotgun shells loaded with any shot in them. When testing a gun for extraction and ejection operations, especially pumps, and autos worked by hand, a full-weight dummy cartridge (loaded with shot) will often function well, aided in the ejection process especially by the heavy weight of the cartridge. That can be a “false reading.” The same gun being tested with an empty shotgun shell or a dummy shotgun shell with no shot in it, having about the weight of an empty shell, may prove not to eject well. That can be for many reasons, including broken extractors and springs, broken or worn ejctors, etc.
As a cowboy shooter using Model 97 Winchester pumps, I keep a few fired cases at home. If I seem to detect a gliche at a match, when I get home I test the gun thorough with both full-weight dummy rounds and fired cases. Sometimes a full-weight dummy will extract well and stay in the extractors until hit by the ejector, and fly out of a gun, and then when tried with an empty shell be hard to extract or if the problem is a worn ejector only, not eject at all or barely fall out of the ejection port. I know that one would think the heavier shell would be the harder to eject, but in many pump and auto shortguns, the opposite is true. Often ejection in these types of guns, of I should say failure to eject, is not due to the ejector, but rather one or both of the extractors being weak or broken. An empty shell reveals a problem exists better than a loaded one, frankly.
I know I didn’t explain that well, but let’s just leave it at the fact that it is often good to have an inert shotgun shell that weighs like a fired case rather than a loaded shell, for testing the functions of a shotgun. Frankly, I prefer an actual fired shell, with blown out crimp, as that is really what your gun must handle perfectly when actually being fired.
With a troublesome gun, you really need both though, as you must be able to unload a loaded gun easily and efficiently if a “cease fire” is called during use, or in the field, if you are climbing fences or doing other awkward movements while carrying a loaded shotgun, so you have to know it will also work with a full-weight shell. Both are just tools for inspection of the mechanical efficiency of your gun, or diagnostic tools to find the cause of problems.