I use 230 military ball everywhere at all times. I only carry it for self defense with regards to humans, and considerations of being in the field, or the game animal I might be hunting, does not play into it.
I like Federal Premium with a 230gr Hydra-Shok. I wouldn't choose ball for anything with a heartbeat. Use a good hollow point. If you need more penetration look for something nonexpanding with as wide and sharp-edged a meplat as you can find.
I saw a tv show on some new 45 bullets that shot a lot hotter (the casings were built for it) and it shot more consistant speed. It was impressive.They shot the bullets out of the same 1911 45 for comparison. Sorry I can't remember what they called the bullets?
I pretty much just use the same ammo I use for home protection as I know it reliably feeds in my gun. I do think that if I was in Grizz country and still wanted to pack my 45 ball ammo would not be a bad idea as it will penetrate better than a hollow point. Having said that life is short and I do prefer to hunt in an area where I really am the alpha predator! I know those of you that are used to it are fine with being around the grizz but this flat lander prefers to avoid animals that have no fear of man and I am just a slow moving meal. Wouldnt it be nice if a gun shot scared the damn things instead of it being a dinner bell?
Personally, I wouldn't carry an ACP for any toothy critters larger than a Mt. Lion. I did some penetration testing in water a couple years back, and in Water my Sig P220 Long slide with Hornady TAP 230Gr XTP in a +P load only out penetrated a Glock 17 with 9mm 110 Barnes XPB in a +P load by about 2".
It can be dificult to find any hot loads for a .45ACP with a penetrating slug. Deepest penetration you will get in a standard pressure load will be with 230gr Ball. If I were looking for a personal defense slug for anything from Mt. Lion to Angry Dogs to 2 legged predators, I'd shoot a 230Gr Federal HST. It's a good modern bonded jhp designed to meet the FBI testing standards for duty rounds.
IF, and this is a big IF, you really want something for toothy critters, Buffalo bore loads a 255gr Hard cast. It's a +P load, so your firearm may or may not be able to run it without modification. It's pushing a 255gr at about 925fps. For me, that just isn't sufficient velocity to ensure penetration through the skull plate of a bear. To give some perspective, Buffalo Bore's Heavy .45LC +P bear load uses a 325gr Slug at 1325 fps, and Buffalo Bore's standard pressure .45LC pushes a 255gr slug at 1000fps.
I've got "Counter Assault" bear deterrent. I've used it twice, once on an aggressive dog (he's not aggressive any more), and once on two small black bears. I've never used it on Grizzly.
Warning, I digress: It was the middle of the night one winter about ten years ago and I was sleeping. My dog was barking so I got up and looked out the front window. I couldn't see anything, but I heard noise on the front porch, to my right, which I could not see. With my head out the window I asked who was there. No answer. I got my 1911 and went to the front door, turned on the porch light and looked out the window by the door. There were two black bears, about 100 pounds each, rooting through a garbage bag my wife put out there. Relieved it wasn't a bad guy, I got the Counter Assault and, still buck naked, I walked out the door onto the porch figuring they'd run at the sight of my pasty white ass. After a quick glance up at me, they went back to work so, insulted, I sprayed them. They ran like hell and tore through a woven wire fence about 30 meters away, bawling all the way. I never saw them again. That was the result I expected merely from them looking at me. Go figure. Anyway, my son, asleep, two rooms away with all doors and windows closed, woke up coughing. I've gotten some of it in me when the wind was wrong. It's horrible.
Anyway, I've studied bear skulls and the brain housing group is not a very big target, especially head on. Add a bunch of hide and muscle, bouncing up and down in a charge, possible poor lighting and the fear factor, and it may be difficult to make a solid hit with a pistol. The Counter Assault, on the other hand, throws a wide net and it throws it about forty feet out and will stop pretty much anything. Even with forward momentum that might bring the bear too you, I doubt he'll be thinking about much when he gets there, other than getting away. The only draw back is if you get stuck having spray into the wind. You'll get it too. But better that than mauled, I say.
Ok, I personally don't have any experience with the SR 45. Much less with +p loads, but It would not surprise me if you needed to replace the recoil spring for them to cycle properly with a +P load. A stiffer recoil spring will help suck up the extra energy from the slide recoiling faster due to the higher pressure of the loads. It will also help to keep the slide from damaging the frame during cycling. The only way to know for sure is to buy and shoot a couple boxes...... That being said, with a .45ACP, you will still be better served with bear spray for bears. For angry dogs, personal protection, and the possibility of a Mt. lion, I'd stick with a .230 HST, or similar modern bonded jhp, or a Barnes XBP. If you have any other handguns, any revolver modern revolver cartridge .357mag or Stouter will be, IMHO, better suited for bears than a .45 ACP. Without another handgun option, the Buffalo Bore will be the best option you have, if your Ruger will cycle it reliably. You might want to do some research before running +P stuff w/o a new recoil spring, and/or what you will want for a replacement recoil spring. I'm not familiar enough with the SR 45 to answer those questions...
While I carry a .357 in the field, Bear Spray should still always be the first line of defense; and If I'm going to leave one protection option behind... It's the .357. Bear Spray will work well on any mammal. Angry Moose, Rabid Dog, Mt. Lion, Bear, or zonked out meth head. It will work on all of them. Bear loads are typically quite different than personal defense loads, and often are not a good choice for stopping people.
ONly down side to a 45 ACP for most folks, is that they would need to wait until the critter is almost on them before they could hit it. If you're not good with an auto loader, perhaps you're better off with a 45 long colt in a wheel gun?