When facing attack by a violent criminal, the reliability of one’s self defense ammunition can be a matter of life or death. If the round doesn’t fire, the crime victim can lose the opportunity to shoot the criminal before that criminal can harm them. Even if the round does fire, an insufficient powder charge could prevent the firearm from cycling properly, leaving that crime victim unable to quickly fire a much-needed follow-up shot. In the worst case, having a double or triple powder charge could cause the firearm to explode, injuring the crime victim and leaving them even more vulnerable to the criminal. To be sure, such failures are quite rare, and I have a great deal of confidence in modern ammunition. However weighing one’s self defense ammo is relatively cheap insurance against such very rare but very serious ammo problems:
Weighing a round of ammunition can tell a shooter a good deal of information about that round. If the round is overweight, it could indicate an excessive powder charge that may damage the gun or even injure the shooter. Or, the excess weight could indicate that the hollow point of the bullet was malformed, and isn’t as hollow as it should be for optimal terminal performance. An underweight round could indicate an improperly small or even non-existent powder charge, which would prevent the gun from properly firing and driving the bullet to the proper velocity. Another possibility is that the bullet is again malformed, but this time lacks the proper amount of metal, leading to reduced performance and accuracy. Or, the round could have an excessively thin casing, which could catastrophically fail when the round is fired and the pressure against it increases by a factor of over 1,000. To be fair, not every problem with a round of ammunition can be determined by weighing that round. It is also true that two problems with a round of ammo, such as an underweight bullet and an overweight powder charge, could perfectly combine to make the round still weigh the right amount, hiding both problem. However, such perfectly combining problems are rare, and weighing ammunition can provide valuable information and help to catch bad ammo, even if it doesn’t always help 100% of the time.
Using .40 S&W as an example, the difference between a good round with a normal powder charge, and a bad round with a double powder charge, is only about 8 grains (or about 0.58 grams). This quite small difference in weight means that most scales used for cooking and other household purposes just aren’t precise enough to weigh ammo. The good news is that scales suitable for weighing ammo are quite cheap and are readily available. For example, I bought an American Weight AMW-100 scale from Amazon.com for about $20 including shipping. That scale has a precision of 0.2 grains, which is more than good enough for weighing ammo. To determine the proper weight of a round of ammo, one can just weigh about 20 rounds and take the average, after disregarding the weight of any rounds that seem grossly different from the norm. For example, I weighed a box of .40 S&W Corbon DPX ammo and found that just about every round weighed in between 217.0 grains and 217.4 grains. Now, I know that if I were to get a round that weighed much more or less than 217.2 grains, something might be wrong with that round. Since I value my life and safety rather highly, I’ll gladly sacrifice a $1.50 self defense round whose weight is off, rather than carry that round in my self defense gun and have to hope that nothing will go wrong.
I would like to again stress the point that modern ammunition is incredibly reliable, and factory errors that lead to defective ammunition are exceedingly rare these days. I trust that my gun will fire more than I trust that my (quite reliable) car will start in the morning. However, with even the best quality control standards in place, some defective ammunition will invariably make its way out of the factories and into the magazines of gun owners. Given that fact, I find it prudent to spend $20 buying a scale, and about 5 minutes of my time each year, weighing the self defense ammo to which I trust my life and the lives of my loved ones.