Just like stated above. Only when pushing it beyond 1200 fps or so.
Not to high jack the thread, and I wish I knew more about this, but my father is very big into cast shooting. I shoot a lot of his 45 acp cast loads. He recently got into rifle cast loading after I got him the Lyman Cast Reloading Book. He's doing something even beyond that now. He recently got a powder coating system from Harbor Frieght and is coating his lead to make them harder than a copper jacket.
Heres a few pictures he's doing. I think he does most of his research on castboolits.com
Pretty interesting to say the least. He currently loading 230gr for his 300 blk. Doesn't have the barrel yet so nothing tested there. He is doing it for his 338 win mag, 45 acp and the 300blk. Don't know what else he is planning. He's a crazy sob.
He hit the .30 cals with a hammer and they broke, rather than deform.