I have a 12 g flechette round made for the US military- guard duty around aircraft- so that you do not shoot up a $30 million dollar plane with an M16.
However, I used to have a EIGHT guage side by side muzzleloader. Problem was, it would kill a deer so far off, by the time you got to it, the meat had spoiled.
Solved that by loading the right barrel with buckshot, and the left barrel with rock salt, razor blades and using waxed paper and string for wadding.
You fired the right barel, and killed the deer. Then fired the left barrel, and started walking. When you got there, the deer had been dressed, the meat wrapped in paper and tied with string, and the hide salted down for tanning.
They just don't make them like that any more, but the game laws now limit you to 10 guage guns.