A ball the diameter of a 12 gauge bore would weigh 1/12 of a pound or 1.333 ounces or 583 grains. That was how shotgun gauges were determined way back in time. The number of spheres of lead it would take to make a pound.
That would be one heck of a projectile to push out a barrel!
"It's all about shot placement" - David (Slayer of Goliath)
"The gun is not the answer to all of your personal protection problems, but when you need a gun, you really need a gun."