I recently linked this video, and because I think A Girl and Her Gun is cool, and because I’m pretty anal about this, I thought I’d talk about Round Set Back, or Bullet Set Back.
OK first things first let’s look at a modern metallic cartridge. So since I can’t find any good diagrams online, we need some homework. Go grab a pistol or revolver cartridge of your choice. Preferably a FMJ training round, as some fancy defensive ammo have some confusing features to prevent this.
Ok so if you stand up your cartridge like a little soldier you have (confusingly enugh) the Head at the bottom (that’s the flat part with the caliber and maker stamped on it, as well as where the primer lives) Then you have the case sides that terminate in a mouth. (Many rifle cases, as well as some pistol cases like .357 SIG have a neck and shoulder before the mouth) In the mouth of the case is the bullet, and the bullet is crimped in place which makes the whole unit feel like one piece.
Now I had to go down all of that to cover some key issues of set back. First is that there is indeed a crimp holding that bullet where it is, second the gun powder that’s inside the case doesn’t fill the whole space. Now we’ve all seen people loading muskets and cannons where they tamp down the powder charge. This is because Black Powder is technically an explosive, and when you compress it it burns rather than explodes.
Smokeless Powder is made essentially of nitrocellulose , which besides smokeless gun powder, you’ve probably seen a magician or science teacher light off a sheet of flash-paper. If you ever see smokeless powder burn outside of an ammunition cartridge its a surprisingly tame reaction. It makes very little noise, and burns leaving very little smoke or ash.
Now this is how we WANT it to burn inside our gun. A quick burst of gas pressure to pop that bullet off the crimp, mash it into the rifling of the barrel and down range to the target. you don’t have a little bit of space for that powder to burn and build pressure it can explode, and certainly it will generate pressure differently than a properly loaded cartridge.
Bullet set back is just that space diapering as the bullet backs into the extra space in the casing.
How does it happen? Well no matter what gun you use it’ll have a feature called a feed-ramp. It might be on the frame of the gun, it might be part of the barrel…or maybe both. When a round gets fed into the chamber of your gun the breech face pushes the cartridge out of the magazine where it crashes into the feed ramp which angles the cartridge into the chamber as the gun goes into full-battery.
This is NOT a gentle action, the slide of the gun is heavy, the recoil spring is powerful, and this all happens FAST. Of course ammo is DESIGNED to handle this, so its no big deal. Its no big deal if you don’t do it all the time. This is one of the big reasons why you hear people say that Glocks explode. This has nothing to do with Glocks, and everything to do with police departments issuing Glocks to people who were carrying .38 Special and .357 Magnum revolvers and not changing arms protocols. In this the officers would be required to unload and clear their gun several times a day. The easiest way to do this is to simply reload the gun and take the round ejected from the chamber and stuff it in the top slot of the magazine…or if the department doesn’t load their guns to +1 capacity, then simply put the chambered round back in the top of the mag until its reload time. This means either one or two rounds get chambered EVERY TIME the gun is loaded. Doesn’t take many of these before the bullet gets hit enough times to pop it free of the crimp and start pushing it down into that case space.
Next time officer friendly needs to fire his gun the gun will blow up…doesn’t matter if it was a Glock, a 1911, or anything else, just there were a LOT of Glocks around, so Glock got the bad rap.
So solutions? Big #1, only unload your gun when you have a reason. When I got up this morning my carry gun was loaded. When I go to bed tonight my carry gun will be loaded, and when I get it out of the safe again it’ll still be loaded. I unload my guns at the range (by pulling the trigger) and when I clean them. #2 If I do have to unload my gun for a various reason I keep track of the cartridge that has already made a trip up the feed ramp. I generally try to re-chamber the same round…and then next time I’m at the range I’ll shoot that round, or I clean the gun the round will go into a box of other rounds that have been chambered 2-3 times. If those rounds don’t look odd, when I have a few magazines worth I’ll shoot them at the range…if they look funny I toss them in the trash, or I pull the bullet and re-load the round.
One of the easiest way to safely keep your gun loaded as often as possible (and keep you from going broke from throwing away a ton of good carry ammo) is to get a lock box or a pistol vault. That way the gun is loaded when you need it, but safe from curious fingers. Another option is to buy a set of calipers and measure the case length of a new factory round, and then keep measuring the rounds you chamber…once you see the round shrinking DISCARD it.
Of course an old fashioned solution is to use a revolver as the rounds are simply dropped into the chamber and held there by the case rim.
Choices Choices Choices!
