Bismuth is a mystery to me, to the point I don't have confidence in it. I suck it up and buy Kent. I have an ample bismuth supply in shells and jugs and don't use it. There's no pleasure in birds dead-to-rights as cripples. My guess is shot brittleness.
When investigating the reports of brittle bismuth shot some years ago, I ferreted out some commentary and laboratory analyses posted on the web that indicate that there were two problems with the production on both sides of the Atlantic in the early years. One was a failure to understand the purity of the less expensive grade of source metal that was initially used and the potential problems therefrom, and the other was poor quality control of the alloying. These together could result in batches with little more than 1% tin (vs. 2% in the patents and 3% in the later commercial specifications) and significant amounts of embrittling contaminants, and it apparently took a surprising while before these problems were sorted out. I've neither experience with nor seen any analyses of the more recent Eley production, but anecdotal reports have it with consistent pure source metals and 3% alloying. In discussions of the making of bismuth shot in Littleton and other shotmakers, a number of individuals report using a 5% tin alloy, but no one that I've read has been specific about any potential increase in malleability and decrease in density of the higher alloy. FWIW, my hunting partners and I had reasonable results with moderate loads of the early production shot in our muzzle loaders, both choked and cylinder bore.
Regards,
Joel
