Sometimes it's necessary to the story to let your hero take a beating or be shot by the bad guys. After all, criminals aren't nice people, and if your hero is involved in catching criminals for a living -- say he is a cop or a P.I. -- he stands a good chance of needing medical care at least once or twice in his life.
Lydia Chin, a P.I. in S.J. Rozan's CHINA TRADE, took a classic beating in that book. Chin didn't miraculously recover from the attack in one day flat. Instead, Rozan portrayed her painful physical recovery over a matter of time, including limiting her ability to perform certain activities for the first few days. Rozan dealt in realism, unlike so many writers who minimize the effects of physical assaults on their characters.
Now let's consider that bullet to the shoulder I mentioned earlier. If you look at the picture on the left, you'll notice there are more bones than muscle showing in the upper arm and shoulder area. Sure, a writer could simply "wing" his victim, grazing the upper outer arm with a bullet and leaving a nice gash there, but little other damage. That gash might require stitches, and it would certainly hurt like heck for a few days, but a tough hero could probably grimace his way through the pain while fighting off the bad guys, especially if he had the biceps of a football player with lots of muscle between skin and bone.
But what if he's shot a little higher in the shoulder? Or what if he's lacking big biceps? And what if he's a size 4 she?? What then? You can probably deduce from the picture that a bullet of any size could do considerable harm to the clavicle, the scapula, or the humerus itself. Damage to any of those bones means our hero -- or heroine -- will be out of the competition for a while.
And what about blood? In these pictures, the red indicates arteries, the blue indicates veins.
"Winging" someone wouldn't cause much bleeding, but a bullet to the inside of the shoulder area could cause massive hemorrhage.
Shooting a character in the shoulder requires some thoughtful decision making on the part of the writer. Can the character be out of heavy duty action for anywhere from several days to several weeks? Can he do his job while wearing a sling on his arm or a figure-8 clavicle strap on his upper body? Will he bleed a little or a lot? Will he experience the minor but annoying pain of a simple gash, or the more exquisite pain of a shattered bone?
It's all up to the writer -- if the scene is to be written realistically.
So, how much damage would a bullet do to you? Check yourself out in a mirror. If you're a small woman like I am, you might be surprised at how little muscle separates skin from bones in your shoulder.