Nothing wrong with a P85, I don't think. I know Ruger updated it a few years later, but if it works, then why mess with sucess? You'll have to check the owner's manual to see if you can use +P ammo safely.
If you are worried about a charging bull, then you should definately run and hide. Barring that, keep that .41 Mag handy with a good-quality hunting bullet.
A full-metal-jacket 9mm round will actually penerate flesh pretty deeply, but the hole will not be particularly big, and 9mms, while having good energy, have less momentum (thump) than a heavier bullet of the same energy. Energy is a function of velocity squared, while momentum is only a function of velocity. A non-scientific unit of momentum is the "power factor", which shooters uses as a quick-and-dirty impact guide, and is simply the bullet weight in grains times the velocity in feet per second. It defines how hard the bullet hits (and how hard the gun bucks when fired), where energy defines how much damage is done. A bullet that hits harder is more likely to make the person being shot aware that he has been shot, and is more likely to have negative psychological effects on the shootee such as panic, fear, flight, and/or surrender.
Using an expanding bullet in your 9mm will make a larger wound and will dump the energy and momentum faster than a non-expanding bullet, so there is both a larger wound channel and a sharper impact. Any expanding bullet from a major manufacturer will do the job well, for they are optimized for anti-personal use. Federal Hydra-Shok, Remington Golden Sabre, Winchester Silvertip, Speer Gold Dot, and Hornady TAP-FPD are all quality self-defense ammunition. It's the stuff the police use.
But they are designed to only penetrate about 12-15 inches of flesh, which is how far a bullet must go in a person to guarantee reaching vital organs. They also typically expand to about .60 caliber (about 15mm) while doing so. This is good for upright humans, not not real good for half-ton bulls!
The .41 Mag will expand more while penetrating deeper, so causing a larger, longer wound channel and dumping nearly twice the energy in the target.
In either case, shot placement is the key. If you're facing down that angry bull, you want to aim low in the chest and, if from a side shot, just behind the shoulders of the animal. That is where the heart and lungs are, and a good hit there will kill the bull fairly rapidly. Of course, if you have the time, go for a head shot and take out the brain, but that's a tough one.
If you load your own .41 Magnums, you can lower the power charge. There is a trick that the handloaders use for this. They buy a bag of rayon (pillow stuffing) at a hobby store, and after they prime the brass and pour in the powder, they use a snug-fitting wooden dowel to tap a wad of rayon into the case. The rayon keeps the powder by the primer for positive ignition and burns up in the barrel upon firing.
I have seen on a reloader's page that he had a load for a 170-grain bullet at 929 feet per second. This gives a muzzle energy of 325 foot-pounds, on par with 9mm loads. Compare this to the hard-hitting Winchester 240-grain hunting bullets at 1250 ft/s, which is 833 ft-lbs.
http://www.reloadammo.com/41loads.htmhttp://www.winchester.com/products/catalog/handgundetail.aspx?symbol=S41PTHP&cart=NDEgUmVtIE1hZ251bQ==You can get set up with Lee Precision loading gear not to expensively. 4-position turrent press is about $90, mechanical scale about $30, carbide reloading dies $33. A brass-trimmer is about $11 (two parts, one is $6 and one is $5) and can be used either manually or in a power drill, a case chamfering tool is $3. You might need a case-expanding tool for cast lead bullets so the lead doesnt' shave off while seating, and that is $13 and mounts in the turrent press. Buy some brass, some primers, some bullets, some powder, and a .41 Magnum reloading guide, and you're good to go. I've listed $180 in parts, plus the consumables and manual. I've used the stuff listed above to load .270 Win rifle cases, and once you set it up it's pretty simple to do. Measuring the power is the most time-consuming part. That case trimmer is a wonderful tool. Dead-on accurate, and if you buy a cheap battery-powered drill it's fast and easy.
The nice thing about the Lee press is that the turrent is removable. Once you set up the various pieces of the reloading dies it the turrent, you can buy another turrent for like $14 and set up the new turrent for a different cartridge. This way you could have one turrent for .41 Mag and one for your 9mm, and just swap them as needed. They pull right out, no problem, no tools.
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