I'm new here and I usually stay out of these kind of discussions because they can get kind of heated. It seems to be different here (hopefully) and I'm not speaking to anyone in particular, but just the readership as a whole, so here goes.
From the time I grew up in bars until part way through my LE career revolvers were still the thing to have "Those darn automatics would just jam on you and get you killed". Eventually things progressed and the guns themselves got better with time also. It's few and far between if you can find a revolver in a cops holster these days, although there are some, mostly in smaller cities. Cops used to have 38 specials with cartridge loops, not even speed loaders, then things seemed to go to magnum cartridges, at least here in parts of the west. It was "knockdown" power that was wanted. I carried 357 magnums and was even issued a 41 magnum at one time and worked with some guys that carried 44 magnums.
We eventually found out the obvious which was that they had too much recoil, muzzle rise, over penetration and most people couldn't shoot them worth a hoot, much less reload one in any kind of a hurry especially under stress. Could you imagine a city, state, or county that would issue you a 41 magnum in todays society. Slowly but surely semiautomatics, new training ideas and techniques began to gain traction, blah, blah, blah......and here we are today.
The point being that things progress, whether we want them to or not or despite how things were in the old days. There is a reason cops don't by and large carry something that holds 5 or 6 rounds anymore, and one of the many
reasons is capacity. As stated I started in LE with a six shot revolver, went to a Browning Hi Power when capacity or 9mm wasn't popular but it worked. I then went to a 1911 due to what we were issued on SWAT. I eventually wandered over to the Glock camp mostly because of capacity. If you've noticed there is a recurring theme here.
I can't think of every reason I've come up with over the years that having a larger amount of capacity can help overcome a lot of scenarios. Don't get me wrong it's not the end all be all thing that will keep you out of trouble or save your tail every time. Awareness, tactics, marksmanship, getting off the X or not being where you really shouldn't be, etc., etc. can probably save you more than having 50 rounds on your person. However we're human and sometimes we get in a predicament or something happens that we really couldn't foresee. It used to be that the biggest thing to worry about was a mugging or strong arm robbery. A J-frame used to be thought of as all you need, "because everything happens in 6 feet or less".
Well things are a changing, it's multiple threats, usually armed threats and threats with better tactics that is more the norm now. I do realize this doesn't happen every time, but enough that it should be a concern to be prepared for. Bad guys are still shooting people at 6 feet or less, but they're also shooting people at a lot farther distances also like across the street, across the parking lot, drive by's, on and on. Would you really want to respond with a J frame with no real sights to speak of, short sight radius (shaking like a dog, understandably so), 5 shots, moving..at least you should be, unless behind cover, slow reload.
Speaking of reloads there was a study done on drug cartel on drug cartel shootings in Mexico. The average distance of shots fired was 50 to 100 yds. IIRC. An inordinate number of deaths occurred during these fights while the deceased was trying to perform a reload. Either they weren't proficient enough or a lot of them had their magazines that they were going to use hit by gunfire and rendered the magazine useless. Admittedly these were rifle magazines carried in chest rigs or bandoliers. I seriously doubt many of you are going to be battling drug cartels in the streets, but my point is that having to perform a reload puts you in even more danger, especially if you're having to do it slowly or more often (no matter how many speed loaders or 6-7 shot 380acp magazines you're carrying) and the more bad guys the more danger. There is something that can be said for getting lead down range in a rather quick manner, preferably accurately. Or what if your 20 rd. magazine malfunctions on your wonder gun, do you have at least one spare if not more, on your person, not in the glove compartment.
I don't remember the statistics offhand but most people in a gunfight including police officers miss their intended target by at least a third of their shots, if not more. So if you have a 1911 with an 8 round magazine and you're attacked by 3 muggers, especially if one or more of them have a weapon, you better be an above average gunfighter, not just an above average shooter, there is a difference. Lets say you are an above average shooter, what about the bad guy(s) that doesn't go down with 1 or even 2 shots in him, happens more often than not. Again a blue haired old lady may prevail with her 1911, J frame, or 6 shot 380, but that's definitely not the norm and I wouldn't put any money on it.
I also believe from experience that them good ole "only real guns shoot cartridges that start with a 4" guns and larger are harder to shoot accurately, through recoil and are harder and slower to get back on target and make successive, accurate hits with. Not that it can't be done, it's just harder for mere mortals, I know, I know, you're not that guy
But seriously most people including myself can shoot a softer recoiling, softer cycling gun more accurately and faster. Which leads to another thing that I believe from experience, that larger calibers or larger cartridges are not the end all be all either.
I'm sure most of you have heard somewhere that there isn't a lot of difference between wounds in human body tissue from one handgun cartridge to another. I can say from what I've seen and discussed with others that this is true. I've been to crime scenes, autopsies, ER's and operating rooms and discussed the subject with Dr.'s and surgeons during the process of being a police officer and an EMT previous to that. Most of them tell me that they can't tell much difference in tissue damage from a 10mm to a 45acp from a 45acp to a 9mm but rifle and shotgun wounds are an entirely different matter. I do believe that with a handgun a certain depth of penetration is important, making bullet choice important and some cartridges not adequate. Lets face it .22 caliber wounds are much more deadly than given credit for, but usually not quick enough to save you in a deadly confrontation, of course some head shots not withstanding. A static head shot is very doable, especially in a proactive role but when it's bobbing weaving and in motion, you're adrenaline is off the chart, it's a lot harder obviously.
I never understood the reasoning behind some choices of carry guns and cartridges. If you're going to bother with carrying why not carry to the best of your advantage. Some people only carry if they think they're going to be somewhere dangerous or only carry a J frame or a small 380 because nothing ever happens here anyway and anything bigger is just too uncomfortable. With that thinking you may as well carry one of those belt buckle size .22 revolvers in your shirt pocket with no reload of course. All this thinking does is give you a false sense of security, thinking I'm doing something. I wish I knew when I was going to be attacked beforehand as I wouldn't be there or I'd have a lot more than a handgun with me if I couldn't avoid it. In my mind defensive carry is a lifestyle or a mindset. Either you get it or you don't, it's either more important than being totally comfortable or it's not, it's either more important to be prepared for myself and my family's safety than to just rely on statistics that stuff just doesn't happen here, or it's not. People usually have health, car, home insurance (if not state mandated) for something that probably won't happen either, but that's a different mindset that seems to be more accepted by society in general. We just don't think things are going to happen to us
As someone previously stated in this thread, the world ain't what it used to be, and our threats are changing and multiplying from when the J frame was king. Maybe being a cop you see the reality of the human mind more or more often than someone who isn't in law enforcement, and the truth of the matter is something probably isn't going to happen to you, and especially if you live in certain areas. However I believe there are a lot of dead or maimed people who wish they had been more prepared for the violence they met whether they believed it would happen or they didn't.
I'm not the authority on police matters, tissue wounds, ballistics, tactics or anything else I guess but I've been around awhile, trained with various agencies, schools, etc. investigated crime and done a lot of different things in my life . I've been out of law enforcement a whole lot longer than I was in law enforcement but I feel that I have some basis to make my decisions on, as right or wrong as they may be. I have made my decision on what to carry and how much to carry based on those experiences. I have come to the conclusion that recoil, muzzle rise and capacity are the things to strive for, obviously in a handgun that fits you and you shoot well. I'm not saying you have to carry 2 guns and 4 or 5 magazines on you at all times or that you can't do this with anything larger than a 9mm. You obviously make your decisions on your own experiences, I won't judge you or badmouth you on the decisions you may make, I may not quite understand them or agree with them but ultimately it's you and your family that will have to live with them.
I'm sure a lot of you will feel differently than I do about some or a lot of this and again I'm not judging anyone or going to try and convince you to believe my thoughts or do things my way as I know it may not be for you, and I have no problem with that. I'm merely laying out how I came to the conclusions I did after having different ideas about guns and cartridges and manners of carry over the years.