It's easy for those of us who have been doing this firearms thing for a while to assume that some bits of knowledge are common to anyone handling/using/collecting firearms, but often what we think is common knowledge is completely new information to many. I've encountered it enough that I think it might be worthwhile to have a thread or a resource where we can collect these bits of knowledge for general consumption. So with that in mind, I'd like to solicit the assistance of the forum in creating some sort of index of these important bits of knowledge that might not be as "common" as we think.
Naturally I'll get the ball rolling. The goal here is to come up with the useful tidbits and refinements to the presentation so that in the end we have something fairly concise and easy to read that will communicate some of these informational nuggets effectively.
Re-chambering rounds:
The act of chambering a cartridge in a semi-automatic or automatic firearm is fairly violent and can have significant impact on the health of the cartridge that is being stripped from the magazine and slammed into the chamber of the weapon. Repeated exposure to this violent process can lead to severe safety and reliability issues. One of the largest concerns is bullet setback. Ordinarily when the primer is struck, the powder in the case burns in a consistent fashion to build the gas pressure that pushes the bullet out of the case and through the barrel. A cartridge that is cycled into the chamber multiple times can actually push the bullet itself further into the case creating enough compression to turn the controlled burn into a detonation. This is, obviously, not good for the health of the firearm or the person shooting it. Further, the act of repeatedly chambering a round has been known to damage other components of the cartridge like the case or the primer that can lead to malfunctions, stuck cases, or dead primers.
How many times a particular cartridge can be chambered without damage depends on a lot of factors including the weapon used, the type of crimp used when loading the bullet into the cartridge case, the quality of the components used in the manufacture of the cartridge, etc. As a result many rules of thumb have evolved over the years to deal with this problem. Since we're dealing in generalities, I prefer the rule that handgun rounds should never be chambered more than twice. After they've been ejected from the chamber for the second time they should be deposited in a dedicated container for training ammo that is used up at the range. With most carry/duty quality self defense ammunition in most handguns (note the use of the word MOST...always inspect your ammunition) this rule will ensure that setback and other damage to the cartridge never rises to the level of causing a problem.
Do you really need to unload the firearm?
For the most part, when a weapon you intend to carry or use in the home defense role is loaded, it makes the most sense to simply leave it alone. Unless you are forced by some administrative regulation to constantly load and unload your weapon, stick to leaving it loaded unless you have a compelling need for an unloaded weapon like cleaning or dedicated dryfire practice. I've encountered lots of people over the years that seem to think they have to clear the chamber of their weapon every time they go off duty or go to bed at night. That practice makes no real sense for most. If you abide by the rule of chambering a particular cartridge no more than twice, you can see that constantly clearing and then reloading the weapon will get expensive. While I don't have empirical data to back this up, there does seem to be some anecdotal evidence that constantly loading and unloading the weapon leads to more potential confusion about the status of a weapon when you pick it up...which has led to tragic consequences. (I didn't think there was one in the chamber!) Obviously every time you pick up a weapon you should do a standard check of the ammunition source and the chamber to ensure the weapon is in the condition you expect it to be in before handling it.