Opinions?!?! I have lots of those, especially when it comes to guns, but I've been teaching people how to use them for 17 years, and I have a pretty good knack for not getting dead.
I'll use "you" because this applies to everybody, not just your son KM.
Firstly, like Ray said, carry whatever caliber you can shoot accurately and quickly. Follow-up shots are important, as is first round accuracy. I tell this to my guys all the time, "We cannot miss fast enough." I'm not a big fan of .380. In my opinion, it's a weak round with bad ballistics. My first SWAT commander always said that if he got shot, he hoped it would be with a .380. However, I have very little use or wound data to back that up, and it's 15 years old. LOTS of people carry them, and like all rounds, shot placement is everything.
I like 9mm, .40, and .45. They are all great pistol rounds, and are easier to come by than calibers like .380 or .357sig. Don't let anyone say a 9mm is weak. They are very fast, so can be devastating. The new powders and bullet designs have removed most perceived advantages of the larger calibers. I like my .40 Glock, but know the .40 round has more recoil and many smaller shooters like the 9mm better, just because of that. 9mm is easier to shoot. I LOVE my .45. I carry a Springfield Operator TRP at work. However, the bullet isn't magic. Yes, it's bigger, but it's also slower. I carry the pistol because I can drive tacks with it. That's because of the design of the 1911, as opposed to the caliber. None of them are greatly better or worse than the others, and bigger doesn't mean better. I know I can carry .45 rounds that move almost as fast as a 9mm, but they'll be +P+ rounds and recoil like a Mo-fo, beating the shit out of me and my gun. Recoil and muzzle flash are why most departments have moved away from the .357sig. It's a cannon because it hauls ass, but breaks guns, and follow-up shots are a bitch. Night time shots with huge muzzle-flash are difficult. 9mm guns,carry more rounds than .40 and .45., so magazine capacity may be a factor.
I am not a huge Glock fan. I think part of that is because that's what our department issues, and a couple neighboring departments as well, so I've had the opportunity to see lots of failures. Glock sometimes does stuff that irritates me, and the blocky shape of the gun doesn't fit me well. However, I'm one guy, and thousands of shooters shoot the shit out of them. Still, my off-duty gun is a .40cal Glock 27.
It's a little fat, and I have the mag extensions on the small mags, because without them, there's not enough grip space and it feels like it wants to flip in my hand. Like any small gun, the mag extension helps with that. The single reason I bought the gun was because I carry it with its 9 round OEM mag, but my reloading source is a 15 round Glock 22 mag. At the time, Glock was one of the few manufacturers where different sizes of different models had interchangeable magazines. It's simple and easy to use. Not the lightest or smallest, but not the heaviest or biggest. It's accurate and has been reliable.
Springfield makes a great gun in the XD series. Lighter than the 1911s, but wider. I have a full size 9mm XD that my daughter competes with. Has the same egos as the 1911, so has a better feel than Glock...In my opinion.
S&W is making huge headway among law enforcement and competition shooters with the M&P series. The Shield is a great little gun, and they fit hands well. They have small, medium and large models, so the can fit the shooter. Remember, a single stack magazine will be less bulky than a double stack magazine. Even Glock has jumped on that bandwagon with the 9mm Glock 43.
There is nothing more or less dangerous about a SA 1911. However, that gun is more involved and takes more training to master. Unlike other models, it has an exterior thumb safety and a grip safety. Gripping a 1911 incorrectly will result in poor accuracy and precision, however with correct practice, most of them are more accurate than their shooters. I know mine are, and I have multiple 1911s.
Right now, Sig Saur is making some very cool guns. I think it's their P238 that lots of people really like. It's been a while since I've shot one, so don't have much info on their new triggers. I had 5 Sigs at one point, 2 .45 P220s, 2 .40 P226s, and a .40 P229. I'm down to the two 226s, because they were both duty guns, and I don't sell or trade duty guns. Too much of a personal connection. Their SA/DA triggers are heavy on the first pull, and the older DAO guns had awful triggers. I've lightened the main springs to help with that. 3lb SA pulls after the 12lb first pull is nice. Lol. Again, I've heard they are better, but I have very little handling time with them, so can't have a fair opinion, good or bad.
Bottom line, go to an indoor range store where they rent guns. Then shoot as many brands and styles as possible. Shoot them until one speaks to you. Fit and reliability are the two main factors people need to look for. Most gun models come in at least the three main calibers, so that's the easy part.
Finally, take gun classes. Lots of them. Most aren't crazy expensive if you provide your own ammo. Like anything, not all instructors are as cool as me, so some give garbage info. I've been to plenty of classes where I discarded lots of material and kept other stuff that absolutely made sense. Use common sense. Anything that sounds like BS, probably is. After taking classes, practice a LOT. I cannot stress that enough. Guns are difficult tools. Improper operation can be very dangerous, or lead to a situation where the gun doesn't work when we need it the most. I've had people roll their eyes when I talk about constantly practicing, but I promise you, if they get into a shooting with someone who does practice, they will lose, for being unprepared.
Once a pistol and a caliber are chosen, shoot and choose acceptable bullets. Don't carry anything "full metal jacket." They pass through with minimal distortion and don't drop energy into the target. FMJ is for practice only. Don't buy specialty rounds like the RIP ammo. That stuff is made by off companies and has shit performance. Stick to reputable manufacturers. Winchester, Federal, Hornady, Remington, CCI, etc. I really like the performance of the CCI Gold Dot ammunition in my .40, and carry Federal Hydrashock in my .45. I've carried Winchester Ranger, which are the new version of the old SXT Black Talons that people claimed were magic, and illegal. Neither of those is true
Our department issues the Ranger for the .45s. However, at my last qual, where we shot our duty rounds, the second round was a failure to fire. Two solid firing pin strikes, so either a bad primer, or something else. Because of that, I'm done with them. I went back to the Federals.
The Remington Golden Sabers are great rounds, but very hot, so recoil is more pronounced. So much that I have a box I've never used. I use the Gold Dot instead.
Hornady makes great bullets, and all of their TAP series would be a good choice. Again, bullets are personal preference. These are not the only choices out there.
Finally, live and breathe the 4 firearms safety rules:
1. All guns are always loaded.
2. Never let the muzzle cover anything you are not willing to destroy. (This means the cat, the TV, an arm, leg, finger, foot, car door, brother, spouse, etc...)
3. Keep your finger off the trigger until the decision to fire has been made.
4. Know your target, what is beyond your target, and your target's surroundings.
Have fun, and good luck.
