Big Bore Lead vs Jacketed bullets

[Rocky Raab]

Several, actually.

For one, most rifles in .45-70 are designed for cast bullets. The leade, rifling and twist rate are optimized for lead.

For another, cast bullets will generally give a bit more velocity at lower pressure than jacketed. That can be important for some rifle designs, where a somewhat weaker design can be offset a bit by the performance of lead.

Finally, almost nothing penetrates better than a hard-cast lead bullet. Most jacketed designs are designed to expand. That may be fine in some game, but in tougher critters like black bear, it is usually a mistake. Deep penetration through the vitals is called for, not a shallow wound.