BBs easier to come by than lead shot these days I guess. I was gifted a bag of lead shot a few years ago. Two of my former customers from my Kaw-Tri shop back in the '70s took over their father's hardware store and were hanging on to the shot their father had used as a re-loading skeet shooter, and a box of fishing line lead sinkers for good measure.
What I do is plug one end of the bar with a wad of steel wool, then pour in the shot gingerly so as not to spill any or overflow the bar, the shot will roll everywhere and escape everywhere ... ask me how I know.
Then plug the other end with more steel wool.
I leave enough room in the ends of the bar to slip in lead sinkers that just fit, instant bar end weights. Add bar end mirrors, and that bar will have a hard time vibrating.