Lead ballast keels come in a variety of construction and alloys. Early limited production and custom sailboats used mostly poured lead ballast keels in poorly inconsistent molds that consisted of scrap lead and alloys all over the place. These were bolted to the keel boss or hull with large silicon bronze or stainless steel bolts. In all my years of experience I’ve found many of these crude keels to as close as any to very soft 1:30 lead. They can be a treasure.
There are also ballast keels which are poured into hollow fiberglass envelopes. Envelope keels are very common if not ubiquitous in Taiwan, Korea and Singapore. They are the cheapest and most unreliable sources for lead as they can include scrap steel, iron, etc dumped into hollow keel with hot lead and fiberglass resin to bond it together. You do not want this crap. Period.
Finally we have production boats with ballast keels that are made by keel companies who specialize in large lead castings that perfectly fit a hull underbody design with bolts precisely stationed so that these big keels mate up perfectly to hulls drilled to accept them. There are only a few of these companies around but the demand is slowing down so they are busy enough. In order to cast keels uniformly and insure perfect mating these companies use between 1.5.- 2.0% antimony in order to control shrinkage and though this is no friend of us bullet casters the percentage with most keels in not enough to cause performance problems.
Locating, handling and breaking down lead ballast keels is another chapter
Good luck be safe
Rick