Self Defense ammo vs range ammo
I don't want to open too many cans of worms, but I have some questions about my practice. I basically learned all of my gun safety, etiquette and practices from my father. But he doesn't know everything, and collectively you guys offer decent opinions.
I have .40 Federal JHP in my gun. The box I bought had 20 rounds so I have two full mags. I choose to keep one in the pipe, so I rack one in, then swap mags, so that my backup mag only has 9. The questions I have are: is there a common practice for doing this, should I be shooting this ammo and renewing it on occasion, and does the bullet/cartridge sustain any damage getting cycled in and out of the chamber? Should I just keep the same ammo in it that I shoot at the range to eliminate the above scenario? Should I practice with the "expensive stuff"? I have never shot any of the JHP through my gun, would it be good to run a couple boxes through?
Thanks up front for the advice, and I apologize if this has been covered ad nausium.
Yes, it can hurt your ammo (and you.)
There is a condition called "bullet setback" that can occur when you cycle a cartridge into the chamber of your gun repeatedly. Basically what happens is that every time the round is chambered, it smacks the nose of the bullet into the feed ramp, which pushes the bullet back into the case a tiny bit.
This shortens the overall length of the cartridge, and can compress the powder if the case was full to begin with. The shortened cartridge can cause problems with feeding and general mechanical function, and the compressed powder charge increases the pressure in the chamber when the gun is fired, which can cause problem ranging from bulged brass to a full kaboom, where some components of the gun give way and are damaged or you are injured.
You can test for bullet setback by simply comparing a new cartridge with one that you have cycled through your gun several times. If the cartridge is shorter, don't do that any more. Make sure that you rotate your ammo, or make it a policy to re-chamber a round only once or twice before firing it at the range.