Looks like #9 bird shot, easy to tell if it is, as it will have a grey powder residue on it "lead dust" and will mash relatively easily, isn't magnetic and no rust of course.
That is what we use for ballast in aircraft where I work.
Seeing that used as ballast would make me fell good as that is the money
is no object, I want it done right way in my opinion. Last time I looked lead shot was about $2 a pound.
I'd assume someone who spent that kind of money
on ballast, it may say something about the rest of the build.