You don’t have to look very far to find a discussion on defensive handgun ammunition. Just last week, on a local website dedicated to the carry community, I observed a heated, almost endless back-and-forth discussion on bullet “setback” in auto-pistol ammunition.
For those unfamiliar with this phenomenon, it refers to a bullet being driven deeper into the cartridge case, almost always due to chambering the same unfired round over and over. An example would be someone going to the range, removing the magazine containing his or her defensive carry ammo as well as ejecting the chambered round, and conducting his or her practice session with target ammo.
When finished, either immediately or after a cleaning session, he or she then reloads his or her defensive rounds, including the previously chambered round. Over time, if the same round is rechambered a significant number of times, it could possibly experience setback from hitting the feed ramp over and over.
In reality, data has shown that this is not a serious problem for most firearms. But certain models and calibers did appear to be more susceptible to this issue than others. Glocks (in .40 S&W) got the most attention when this condition first appeared, but they are by no means alone, especially when heavier bullets are involved and re-chambered half a dozen times or more.
This makes sense; since overall bullet length remains the same, a heavier bullet is already seated deeper, resulting in a decreased case volume. Thus, with 0.010 inches of setback a .40 S&W 180-grain bullet will yield a much higher increase in internal pressure than a 155-grain bullet with the identical reduction in overall length. But again, unless you are reloading the same cartridge over and over again, it is not something you should agonize over.
All that being said, what should you do if you think that you might have such a problem? When I contacted several technical experts familiar with this issue, they confirmed that even in those particular guns that are known to experience setback, there are some simple and easy ways to deal with it.
First, to see if you even do have an issue, just measure (if you have a micrometer) the suspected round (the one you’ve chambered multiple times) and see if it is significantly shorter than the “minimum recommended Overall Length (OAL)” that can be found in any good reloading manual (even online). Safe rule of thumb? More than 0.05 inches below minimums, I’d toss it.
Don’t have a micrometer? Then simply set the potential offender upright between two never-chambered factory rounds. Now set a straightedge, ruler or even the edge of a business card on top of all three. If you can see significant “daylight” between the middle round and the other two (the thickness of a penny or more), then, once again, just chuck it. Why take a chance of a “kaboom” for the price of one round?
And in order to prevent the problem in the first place, try middleweight bullets: 124- to 135-grain in 9mm; 165-grain in .40 S&W (note: Hornady uses a tight crimp and cannelure in their 175-grain Critical Duty round, which should resist setback). There have been few reports of setback issues with .45 ACP ammo, perhaps because they operate at substantially lower pressures than either 9mm or .40 S&W.
Beyond that, carry any good quality, name-brand defensive ammo that you have function-tested in your gun, and sleep well.
