Here is a link to the construction of a few .458s
http://shootersforum.com/big-bore-le...thickness.html

Notice how thick the plating is on the Speer. I will post the cross section pic of the bullets when i can find it. New Barnes Originals 300gr Spitzers are actually .035.

A thick jacket can be a benefit but sometimes they can be less accurate too. A lot depends on the jacket material and lead purity. Thinner jackets and a pure lead cores are often very accurate and very effective on game if they have enough mass.

I haven't shot the Speer 458 but i can tell you the Rems, Hornadys and Sierras are far more popular than the Speer 458s.....At least with Savage owners shooting under 200 yards. It might be the concave base hurts accuracy at those speeds.