There is definitely extreme penetration. Effectively, with that 380 grain cast bullet, it would mean you never recovered a bullet from game. No wonder the old cartridge worked so well on bison.
Man, it isn't even fun testing cast out of the 45-70 at any speed. They just lance all the jugs and you end up with a bullet you could almost reload again!
And they laughed at Keith? I remember some of the articles from the 1960's ridiculing Jack Lott and Elmer as dinosaurs. The problem was of course for being able to punch an over .40 caliber hole into, through and out of the other end of a trotting south bound elk in the trees from the wrong end with no muss, no fuss.