This came up in another thread and rather than divert that thread any further, I thought I'd just make a new thread on this subject.
The issue is the problem of setback from chambering a round repeatedly and direct chambering that some have opined will lead to extractor failure.
So, why does any of this matter in the first place? Well, for those that never have to unload their carry ammo, either to leave their gun in a vehicle, or unload to shoot, etc., it isn't a problem. But for those who have to unload their gun for what ever reason, especially on a daily basis, we may need to be aware of some potential problems with our methods.
Rechambering and setback:
I personally have tested an M&P, Sig 226, Beretta 92FS, H&K USP, and several 1911s and they all produce setback. In case the term is new to you, setback is when the bullet is pressed back into the case. The problem with setback is it can raise the chamber pressures enough to cause damage to the gun.
While guns can be tuned to minimize, if not, eliminate setback, most of us have out of the box stock guns, and they generally produce setback.
Setback is caused when the round feeds into the chamber. Typically, the slide picks up a round from the mag, drives it forward and the nose of the bullet contacts the feed ramp. That's where the trouble begins. If a round is only chambered one time, the setback is very minimal or may not occur at all. But as we rechamber that same round, things get progressively worse.
Probably most of us load a gun by putting a fully loaded mag in the gun, drop the slide to chamber the top round, remove the mag to insert a round to top off the mag. When we unload the gun, we drop the mag, rack the slide. When we reload the gun, we already have a fully loaded mag so we insert the mag, rack the slide (if it's not already locked back) and the top round is chambered. The mag is removed and that loose round is inserted in the mag to top it off. This process rechambers the same two rounds, every other time of course, everytime we reload.
If we do this daily, for two weeks, each round has been rechambered 7 times! I.e. the two rounds have been setback 7 times! From my tests, the rounds seem to hold up for a chambering or two and then they really start to move.
One alternative is to rotate all the rounds through the mag, but that is a bunch of trouble. The mag has to be completely emptied every day, so the last chambered round can be put on the bottom of the stack. But that really just postpones the inevitable.
Direct chamber loading:
Direct chamber loading completely eliminates the setback issue, so rounds can be chambered this way over and over again with no setback whatsoever. Here's how that works:
Starting with a fully loaded mag and one extra, loose round, the slide is locked back and the loose round is dropped into the chamber. The slide is then dropped. This is where some contraversy occurs. Some say that this is hard on the extractor because it forces the extractor out over the rim of the case and doing this will eventually break or damage the extractor.
However, if you look at the loading instructions for a Beretta 92FS and PX4, you will see this loading method described as a viable loading method and there is no indication that it is harmful to the gun. I have been using this method for quite a while with my Sigs and have seen no ill effects. But to be sure, I called Sig Sauer and asked them about this issue. Without hesitation, they said there was nothing harmful about it and even said that the direct loading method was used by many people as a way to have a full mag and a chambered round in the gun.
So what we know is that chambering a round from the mag will produce setback in most guns. So it would be a bad idea to chamber the same round more than once or twice using this method.
We also know that the direct chamber loading method will not produce setback, allows rounds to be chambered many times safely, and is fine for Beretta 92FS, PX4, and Sig handguns. That does not mean it is ok for all guns. So before you use this method, you should talk to the manufacturer of your gun.