I picked up some budget-level .308 caliber bullets recently. They came packed in 100-count plastic bags and were labeled as being 147-grain, full metal jacket, boattail design, with a cannelure. Clearly not match bullets, but intended for volume shooting, they were nearly half the price of offerings from the major bullet companies.
The bullets look great, but before working up some loads for these shiny new projectiles, I couldn't help wondering how much quality control was involved in their manufacture. So, it seemed an easy test would be to measure the weight variation present in a handful of them.
I'm no statistician, but I know it's necessary to weigh a considerable number, likely at least 30, before arriving at a reasonable conclusion. A good rule of thumb for any sampling/measuring exercise is to keep sampling until a classic bell curve is formed. Then, we're likely to see a valid statistical result.
Using a laboratory-grade scale capable of measuring 0.02 grains and then rounding the result to 0.1 grains, I weighed 50 bullets and got the result shown below. The plus and minus symbols indicate bullets heavier or lighter than the indicated weight. Clearly, these bullets are a bit heavier than the advertised 147 grains, with the majority falling between 148.0- and 148.3 grains.
With a weight difference between the two extremes of 1.0 grain, that's not too bad for budget bullets. But then I realized I didn't have any figures to compare this against. And that's when I started down a rabbit hole. Just how consistent are the weights of modern rifle bullets?
I didn't have anything comparable to these bullets in my collection, so I looked for some simple, basic hunting bullets, i.e., no polymer tips, no boattails, no bonding. Settling on some Hornady .30 caliber, 150-grain round nose, flat base bullets, with cannelure, I weighed out 50 of those as well.
That was surprising, as I really didn't expect a level of consistency showing just 0.5-grain as an extreme spread. To me, that seems like a great result for what is a low-cost, short-range hunting bullet.
Of course, then I just had to try a match bullet. A look at my bullet shelf turned up some 6.5mm, Sierra 130-grain, Tipped Match King bullets. These have always shot well in my Creedmoor, so I weighed 50 of them with the following result.
This certainly suggests Sierra has weight consistency figured out in their TMK line. And let's remember these are complicated, three-component bullets in that they have a lead core, a gilding metal jacket, and a polymer tip. After all, it would seem reasonable that the more complicated the bullet is, the more difficult it is to keep weight consistent.
That led me to think about bonded, three-component bullets, like Nosler's AccuBond, a hunting bullet with a great reputation for accuracy and weight retention. Not only do they have three components, but they also undergo a bonding process that "attaches" the lead core to the jacket.
I found an unopened box of .30 caliber 165-grain AccuBonds in my collection and weighed them with the following result.
They came in a little heavier than advertised at around 165.6 grains, with enough outliers to make an extreme spread of 0.7-grain. Can we assume the more elaborate construction is responsible for the outliers? Maybe.
Okay, one more then. I decided to weigh the simplest bullets of all, mono-metal lathe-turned bullets constructed only of copper alloy. Barnes is well known for producing these bullets, and I have most of a box (43) of 6.5mm 130-grain TSX Flat Base bullets. These bullets count on the hollow point in the tip to initiate expansion, so they really are single-component slugs.
My weight sorting produced the following result.
Overall, they were a touch lighter than advertised, with a 0.6-grain extreme spread—an interesting result.
After all this, I've learned more about the weight consistency of modern bullets, including what great results look like. Overall, these findings suggest manufacturers are doing a really great job of producing consistent-weight bullets. However, as for a practical application, I'm not convinced there is much of one. Even the 1.0-grain spread of the budget blaster bullets that started this journey isn't enough to create a practical difference in trajectory except at the most extreme of ranges. And since those outliers are only 0.5-grain away from the average, it makes even less of a difference. Additionally, it's important not to extrapolate these findings too widely, as the numbers could change significantly with the next lot number.
What we can perhaps say is that modern quality rifle bullets should have less than 0.5% variation in weight. All the above made that standard, except for those budget bullets, and they didn't miss by much. Now, if you want to weight sort the bullets you use, go ahead; at least you'll have something to compare the results to. I'm just going to shoot all these bullets.