The SOCOM is limited to rifle bullets that are made to preform at velocities greater than the maximum velocity one can get from a SOCOM....so most any bullet isn't going to expand to any great extent...
There are a few .458" bullets that perform very good at SOCOM velocities. I have tried the Hornady 300 grain HP and it does just great. I'm going mid-1700s with it, and having used it in the .45-70, chose it because I noticed that it had a tendency to expand too rapidly if pushed beyond 1900 fps. The Speer Unicor doesn't expand as much but retains damn near all of its' weight.
The Sierra and Nosler versions ought to do well at SOCOM speeds
Most of the bullets designed for the .45-70 are intended to expand at lower velocity. Most factory loadings are under 1800 fps, and with the heavier bullets, 1300-1400ish
It is able to push 350 grain LBT cast at what many would consider ideal velocity. With this bullet design, expansion is not needed.
