I'm not sure what your "dump" reference means, but I think I understand the rest of the question.
First, in my experience with U.S.-made guns, most shotguns will have acceptable ammo types stamped into the metal of the barrel, near the receiver (example: "2.75 and 3-inch shells only"). Normally, in any shotgun gauge or caliber, a person can safely use a shorter shell in a longer chamber of the same bore size. For instance, if you have a 12 gauge shotgun with a 3-inch (75mm) chamber, you can safely use 12 gauge 2.75-inch (called two and three-quarters-of-an-inch, or 70mm) shells in it. If the weapon has a recoil- or gas-operated semi-automatic action, the shorter (and usually lower-powered) shells may not supply enough energy to cycle the action and load the next round into the chamber automatically, but it will still fire safely. The same is true of the longer 3-and-a-half-inch 12 gauge shotguns, usually used for long-distance hunting of heavy birds like geese or turkeys. You can safely fire the shorter 2.75 inch and 3 inch shells in it, although you might have cycling problems with low-powered ammo. Never mix bore sizes between gun and ammo, like attempting to fire 20 gauge shells in a 12 gauge gun. Never chamber a LONGER shell that your gun is intended to use; sometimes it seems like it will "fit" into the gun's chamber, but it will not have enough room to safely unfold the end crimp when fired, and the increased pressure will almost certainly wreck the gun and possibly injure/kill the shooter (or others nearby).
For the final word, check the user/instruction manual that comes with the weapon; it should have a list of acceptable ammo types for that weapon. If you don't have the manual (used guns sometimes don't come with one), some manufacturers have posted copies of their manuals online, and some folks have made and posted electronic copies for the out-of-production guns.
Finally, if the gun is very old, it should be examined for general safety by a certified gunsmith prior to being fired. Very old laminated or "twist" barreled guns, or any gun that was intended for black powder use should NEVER be fired with modern smokeless gunpowder shotgun shells.
The Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) has a handout that lists unsafe gun/ammo combinations; it can be found here:
with the shotgun info listed on page 3.