
With more and more airgunners shooting at ever longer ranges, pellet consistency becomes increasingly important. But what should we expect as consumers from the pellets we shoot?
Dedicated Field Target and Benchrest competitors have long sorted their pellets. So there’s some experience that sorting by weight – and by head size, too – maximizes downrange accuracy.
Measuring pellet head diameters is easy. Just use a Pelletgage – it’s available from AOA.

First, let’s give the pellet manufacturers some congratulations!
Given that they’re mass-manufacturing and selling pellets for just a few cents each, the quality is really amazing. It’s clear to any enthusiast that the overall quality and consistency of our pellets has improved greatly over the years.
The head diameter of a pellet determines how deeply it engages with the barrel’s rifling. Variations in this degree of engagement can alter the Muzzle Velocity and result in downrange accuracy issues.

The photograph below shows two pellets of the same type. That on the left is un-fired. The one on the right has been fired. Grooves caused by the pellet’s head engaging the rifling are highlighted by the arrows. (The skirt also shows some grooves, as you can see).
As a result of a TON of measurement, we find that – on average – pellets work-out to have head sizes slightly larger in diameter than the nominal barrel diameter.
In fact, pellet head diameters average 0.51% larger than the caliber. This makes sense as – if the head diameter were to be smaller than the bore, the head would not engage with the barrel’s rifling and accuracy would be terrible!
The average difference in diameter between the smallest and largest pellets in a tin can be as high as 2.5%. But typically it’s more likely to be around 0.5%, as we can see here from this chart.

Generally, larger calibers tend to have head diameters that are proportionally greater, as we’ll see below.
Furthermore, heavier pellets in any specific caliber will tend to have head diameters that are larger. Lighter pellets in a specific caliber tend to have head diameters that are closer to the nominal bore size.
Take look at this chart…

As this chart shows, the percentage by which pellet head diameters measure above the nominal bore diameter increases with caliber. So – for example – .22 caliber pellets have greater head engagement in the rifling than do .177 caliber pellets.
It would be reasonable to expect that rifling depth is likely to be greater in larger bore diameters, so that makes sense.
But as we can see from the next chart, the variation in head diameter between the smallest and largest pellets in a tin tends to be greater in .177 cal than it is in .22 caliber.

That tells us that – on average – there’s likely to be somewhat more benefit to sorting pellets if you use .177 caliber than if you shoot .22 cal. However, in each caliber a good number of pellets tested showed a difference of 0.02 mm – that’s about 8/10 of a Thou – between the largest and smallest in a tin. It’s the outliers that make the difference!
If we take the same data and express it as a percentage, the average difference between largest and smallest is less in .22 caliber than it is for .177. This is basically because a similar level of consistency is being applied to a different diameter. (The larger the bore diameter, the smaller the percentage).

All-in-all, this analysis demonstrates remarkable consistency in airgun pellet head diameters. However, it also demonstrates that – for best results downrange – sorting pellets for consistent head diameters is extremely valuable.
Consistent downrange accuracy requires consistent pellets. Somehow I very much doubt that any top competitors in Extreme Benchrest fail to sort their pellets!
For information, the pellet test data analysis here is based on measuring a total of 3,800 pellets. As you can see, there’s more data for .177 and .22 cal than for the larger calibers. But the general trend is pretty clear.
If you’re interested in accurate shooting and don’t have your own PelletGages yet, it’s time to buy some! They’re available in five common airgun calibers. There’s .177 and .22 calibers, of course, together with.20 cal, .25 and .30 caliber. AoA has them in stock…



























































