It looks similar to the metal jack you attach a vehicle tire compressor to? It even has the bump in the center that would release the air into the tire?? Maybe it is just used to adjust the air from tires by releasing some?
Nokta FoRs Gold, a Gold Cube, 2 Keene Sluices and Lord only knows how many pans....not to mention a load of other gear my wife still doesn't know about!
Unfired muzzle loader bullet. Possibly a Buffalo Bullet Co brand bullet.
Crosshatching holds the lube in place.
They did make them in other calibers besides .54 as well.
You'd have to measure and weigh the one you have to see what it is.