I purchased an Armalite AR-7 a few years ago, from an advertisement in the Sunday newspaper for $85. Sold it at a Gun Show for $325.
OK I will throw my .02$ in on this subject.
I started carrying at the ripe old age of 20. And have carried everyday of my adult life. Never missed a single day, not once, not ever.
I am 52 now. Wow, that seems odd to say that I am a 50 year old guy, I don't feel a day over 25!
In those years I have carried the following in no particular order;
A Colt Double Eagle Officers Model in .45 ACP, a Colt Mustang in .380ACP, Glock 23 .40S&W, Glock 26 9MM, Taurus PT111 Slim 9MM, Kel-Tec PM-9 9MM, Ruger LCP .380, Beretta Nano 9MM, Ruger LC9 9mm, Beretta Pico .380ACP, S&W model 36 .38SPL,numerous 1911 in 9mm, .45ACP, and even .357 Sig.
Several Taurus and Rossi .38 and .357 revolvers. And numerous .22 cal revolvers, pistols, and even a folding rifle for a few months once.
In those years of carry I have learned two things; 1.) If you aint prepared to use it don't carry it. 2.) If you don't test it regularly it will fail for you when you need it.
While I have never needed to use my weapon on a human, I have had to use it on other "aggressors" such as a wounded hog that came out of nowhere, and several elongated scaly creatures that start with an s that others seem to think are pets.
I have also dispatched wounded animals on the roadsides hit by cars, up to a cow, and as small as a tiny dog.. In every case the weapon has been more than adequate for the job and the weapons have performed perfectly with a few notable exceptions involving my not having cleaned a weapon often enough and it being unreliable due to lack of maintenance.
Also some of the guns mentioned above never proved to be reliable and thus were only carried for a short while. But like my two lessons state if you want to bet your life on them you have to be ready and willing to use them, and you need to have maintained them and practiced enough that you can use them well.
As I age, the number of shots does not matter quite as much as it used to, and the weight and recoil of the gun matters more to me. While I still enjoy shooting .44Mag for fun I would never carry that boat anchor unless I had nothing else. A nice .380 or 9MM in somewhere around 7-12 rounds is plenty of gun for me. And if you can make it thin and light as well that's even better.
Put some sights that I can see on it and I'm a sucker, take my money now.
I have kept a sweet 1911 Officers model in 9mm that I love to shoot and carry occasionally. But it's too heavey for everyday
Anyhow thats my .02$.