Oblasterate
.
Seriously, a Freedom Arms won't care either way.
I'm not 100% sure which is doing more pressure. You can get more bullet speed for the same weight with unjacketed lead...that's why Remington gets the same speed out of a LSWC-HP 38+P 158gr as Speer gets with a 135JHP.
I'm also not convinced pressure is "everything" in this specific question.
Consider: we know that magnum 125gr JHPs at full-house pressure ate early K-Frame 357s. We know why: it was all about the "hit speed" at the forcing cone. Run 158gr at the same pressure, even jacketed, and you soften the hit right there at the beginning of the barrel because the round isn't going all that fast YET at that key weak point on a K.
OK, now back up and use 125gr lead slugs at 1,400fps. Better gas-check 'em of course or leading will be a monster, and as a defense load that just doesn't make sense (going too fast if soft lead, no expansion if hard) but set that aside and let's say somebody shot scads of such silly things.
Would the lead hit the forcing cone lighter than copper jackets would?
I suspect so but no proof. I suspect the lead would deform more on impact with the key K-Frame weak point and hence not deliver as much hit to said weak spot. BUT I'm not sure and since the load is just silly we'll probably never know.
Interesting to ponder though.