Hit pretty god damned hard...
I gave the boys at the gravel pit a bit of a lesson in applied ballistics the other day. As luck would have it, a very common modern hunting round, the ubiquitous .30-'06, generates about the same muzzle energy as one of my big bore muzzle loaders, about 2,900 foot pounds. This is with the standard '06 load of a 180 grain bullet at about 2,700 fps. This particular muzzle loader, a .72 caliber, launches a round ball of 583 grains at about 1,500 fps, for the same 2,900 foot pounds of muzzle energy.
We were shooting at one of the Caldwell "magnum rifle" gongs at about 100 yards, like this one. Our chains ar a lot longer now, so the gong hangs almost down on the ground - we found that modification to greatly enhance durability, with more "swing" to absorb the impact. It's otherwise identical to this one. The gong is about ten inches in diameter:
So one of the guys starts in on it with his M 70 in .30-'06, shooting from various field positions, and having no trouble ringing it. Actually, it's a pretty solid "thwack", and the plate jumps all over hell. Pretty impressive, really. At least until I loaded up the .72 and went after it...
That darn thing hit it so hard that it knocked the gong around for one full lap of the cross bar, as it dislodged the frame from under the big rocks we place on its legs to hold it in place, upending the whole works.
What a stark display of the differences between how "energy" is generated by two entirely different philosophies. One, light and fast, the other heavy and slow. Some argue that "energy", whose calculation squares velocity, actually overemphasizes velocity by doing so. "Momentum" calculations do not, thereby assigning equal weight to mass and velocity both. Watching this little demonstration sure served to lend some credence to the "momentum" argument.
The rifle:
.72 round ball and .308 dia, 180 grain spitzer:
