Matt's initial post is on point for traditional expanding hollow point bullets (assuming we're talking about defensive pistol ammo here). I've been using some of the Lehigh offerings though and find them to be an exception to that traditional wisdom, because they are a very unconventional bullet.
I've only used these on smaller animals (nothing bigger than coyote) and test media, so take my comments with a grain of salt, but my media testing has been pretty extensive and I've drawn some conclusions for myself on these bullets. (I'm a test and development guy by profession, and have been testing bullets for myself for about 20 years so I feel I've developed a pretty good handle on what can be learned from various test media and what can't.) Just putting that out there to put these comments in the correct context. I urge anyone considering these to evaluate them for themselves.
I've spent the most time with the Lehigh 9mm bullet line, so I'll comment on those:
- the 115gr Penetrator does what it claims by penetrating deeply in both hard barriers and meat. However, peripheral damage (like we want a hollow point bullet to create) is not very extensive around this bullet, and in my experience it performs more like a hard cast flat nose bullet than anything else. It also didn't shoot as accurately in 4 (or 5?) different pistols in both 9mm and 357 Sig.
- the 90gr Defender bullet impressed me the most and is what I carry now in 9mm. This bullet works best with high velocity, so +P+ loads are appropriate, but the light weight makes it fairly easy to shoot accurately. It penetrates hard materials like auto body panels, aluminum plate, etc better than most other 9mm bullets, which is to be expected from a light fast bullet. The impressive part to me was the penetration in soft test media and meat; it performs on par with 147gr HST and penetrates farther than some common loads like the 115gr Barnes and 124gr Gold Dot +P. Peripheral damage from this bullet is a bit different than a typical hollow point in my experience, but adequate. I like the Underwood 9mm +P+ load of this bullet, at 1550 fps from a G19.
- the 65gr Defender bullet is capable of impressive velocity, but penetration in meat and soft media is fairly shallow. It acts more like a traditional 90gr JHP in 9mm, dumping it's energy rapidly even though it remains in one piece. I'd consider this one further if I carried a 380, but I don't and have no plans to.
A couple other thoughts - all of these bullets are solid copper and non-expanding; recovered fired bullets from soft test media could be fired again except for the rifling marks.
- the ruger ARX (Polycase) line appears superficially similar, but do not perform nearly as well; I tested some of those and quickly lost interest.
Hope that helps.