.02$ on the old post.
Ever since I found an article in the early 90s on the lyman 358156 I have been shooting those. 165 with the gas check, it has been around since at least the 50s as the Thompson gas check bullet.
As RMc stated earlier, the flat nose is what acts as the "destructive agent". Although the flat is only .25, the bullet acts completely out of proportion to its size. A grain below max with 2400, and the bullet clocked at 1350 out of my 6" blackhawk.
I have had good luck using it on deer, but I have only shot it out to 50 yds. The slugs don't stay inside the deer either. Super accurate and it definately doesn't leave you undergunned.
I think that cast performance has a similar bullet in the same weight range if you don't cast.
Cheers and happy New Year.
Tom