woods defense
The woods defense bullets (hard cast slugs) are NOT intended to expand. By design, they are penetrators, gaining some wound channel (maybe) by their flat meplat, but first and foremost, penetrating through hair, fur, hide, dense tissue and bone to the vitals of critters big enough to cause harm. Handguns in general are underpowered for use against that type of threat, and one of their short comings is lack of pentration due to low velocity and the wide assortment of handgun bullets that ARE intended to expand. The hardcast family attempts to address that.
I'm not entirely certain, but I'll add that if all is equal, hardcast lead slugs will have a tad higher velocity than a copper jacketed slug of equal weight.
It was stated earlier that "though lead is soft, without that hollow cavity, they won't deform". That is debatable. I'd offer that a .357 JSP will indeed "deform" but it may or may not "expand", and a JHP is subject to the same speculation, though expansion might be more expectable. There are lots of examples of soft lead roundballs from muzzleloading rifles taken from game animals that deform and expand, forming flat near disk like shapes. I've taken .32 roundballs from small game that certainly had deformed, and flattened into wide disk shapes larger than their initial diameter. BUT, that is at muzzleloading RIFLE velocities. Ballistic gel shots from BP handguns show deformation of both roundball and conical, but often not much.
As noted by 44AMP, JSP's are intended to expand less than a JHP. Accordingly, penetration should be a bit higher. But the softer lead core of a JSP is a bit of a liability on large boned critters, and will probably not equal the penetration of a hard cast lead bullet of equal weight and velocity.