Often times they say SP is bad. But it doesn't look bad at all when I see it being used in ballistics gel. So this leaves me a bit confused.
The confusion is understandable, and brought about by the all two common tendency to shorten names, which can leave out vital information.
"SP is bad"..ok WHAT SP is "Bad" and why? There's a LOT of different bullets with much different construction and terminal performance under the broad heading of "SP".
There are SP "varmint" bullets and there are SP bullets built for more controlled expansion. And they can be the same weight, so just because its a 55gr bullet doesn't mean anything beyond it weighs 55gr.
I understand (but don't know for certain) that the ammo being sold as "personal defense" class stuff is not loaded with "varmint" bullets. They are supposedly loaded with a more controlled expansion kind.
I know for a fact and personal observation over decades what "varmint" bullets do, and don't do, out of .22 Hornet, .221 Fireball, .222 Rem, .223 Rem, and .22-250. There's about nothing better when your live target is 5-50lbs. When your target is larger, things change.
A 55gr SP meant for shooting woodchucks will do what it does on bigger things (like people) but what it does isn't certain to be enough to stop a determined attack (with a single round). It MIGHT, it probably will, BUT, its not certain in the way a round that penetrates deeper is "certain".
Penetration in gel is a method for ROUGHLY comparing performance, but real people are not gel.
Penetration is the bug-a-boo with a lot of people today. Probably because too many people live too close together....they're worried about the neighbors, and rightly so, in many cases. HOWEVER, there's no free lunch, and its nearly impossible to make a bullet that will NOT go through walls but will go through people, deeply enough, and do it under every possible real world set of circumstances.
That bullet (whatever caliber & speed) that meets all the "recommended" penetration requirements, can (and has) failed in the real world when the specific circumstances require it to do more than the stated requirements.
I keep coming back to the 9mm JHP that "failed" in the Miami Shootout. It did everything it was spec'd to do. BUT additional real world factors changed things enough that what it was spec'd to do wasn't enough, that day.
If gel test performance of a certain bullet is enough to make you feel good, remember to get that EXACT SAME BULLET or you won't get that exact same performance. A bullet built to take out a deer, (or a man) can be the same size weight and speed as one built to take out a coyote or a prairie dog. They might even LOOK identical. Make sure you know what you've got, and what's its best at.