I’m not completely certain what you’re asking here, but there are a few possibilities.
Muskets and some other early firearms were muzzle loading. Meaning you’d actually pour powder down the barrel, and then follow it with a bullet. Tap it all down, and then use wadding to keep the bullet from migrating. Read: “falling out.”
Similarly, harpoon and spearguns. These vary, some harpoon launchers use propellants, while spearguns use, I think, pneumatics. I don’t know a lot about these, but, they do exist.
I know the OSS was working on a grappling hook attachment for the M1911 during WWII. The idea was you’d mount the hook into the barrel and propel it up with a blank cartridge. I don’t know if this was ever used in the field, but today it’s a curiosity, so something must not have worked out as planned.
Some single shot grenade launchers, such as the Russian GP25, use a muzzle loading arrangement.
Normally speaking, sticking something in the barrel of a gun will result in an obstruction. Which is the technical term for, “causing the barrel to explode in your hands.” So, simply grabbing a rod, spear, whatever, and cramming it down there will destroy the weapon, with a decent chance it will tear your hands into meat confetti in the process. Loading it with blanks can serve as a propellant for something else, like the grappling hook example above. But if the foreign object doesn’t properly fit the barrel, then you could find yourself with the chamber detonating, which is even more likely to destroy your hands.