The Big HAM Slugs Test. Part One. There’s No Single BC Value For Slugs
With so many airgunners – and airgun companies – so excited about shooting slugs, it’s important to understand that there’s no single BC value for slugs.
I’ll say that again for emphasis because this is not widely appreciated. There is no single BC value for slugs. When calculated using the G1 drag profile, that is…
Yes, slug manufacturers are obviously keen to promote a headline BC value for slugs they manufacture. And most people feel that higher BCs must be better. After all, the higher the BC, the more energy is retained downrange. And that must be a good thing, right?
Even in HAM’s industry-leading Ballistic Coefficients database, we only publish one BC value – we calculate that at 30 Yards downrange. We do that for simplicity to present a representative value.
But the point of today’s post is to emphasize that the BC value for slugs – and pellets too, for that matter – is not a single, fixed number. It varies due to a number of factors, at least when the G1 model is used for the calculations, as everyone does.
The BC Value For Slugs Changes With FPS
One major factor for changing BC values is the speed at which the slug is traveling. BCs will generally be higher at higher FPS.
So, a more powerful air rifle will generally provide a higher BC value than than for the same slug fired from an airgun of lower power.
Not only that, but – obviously – the velocity of a slug (or pellet) changes during its’ flight downrange. It slows down and so generally does its Ballistic Coefficient value.
So can we prove that? Well, yes, by measuring the velocity of slugs (or pellets) at multiple different distances downrange using Labradar and then analyzing the data using a sophisticated spreadsheet constructed by HAM Technical editor Bob Sterne.
For this Big HAM Slugs Test, HAM Contributor Matt Coulter and I worked together. We used one standard air rifle, Matt’s .22 caliber CaliberGun Cricket 2 Tactical.
This is a known excellent air rifle, both powerful and accurate. It earned a massive 93% and HAM Gold Award on test.
Data was recorded using a Labradar Doppler radar unit and analyzed using an Excel spreadsheet.
All shooting was done by Matt at his 50 Yard home range. I operated the Labradar, recorded and analyzed the data.
We tested 13 different types of .22 caliber slugs from multiple manufacturers, with weights varying between 20 and 30 Grains. In addition, we included a “control test” using a known-outstanding type of pellets: 25.39 Grain JSB Monster Redesigned.
Examples Of Changing BC Values – 21 Grain H&N Slugs
There’s a ton more data to come from the Big HAM Slugs Test and we’ll cover that in future posts. But today let’s look at how the BC value varies with changing velocity downrange for a few sample slugs, together with the JSB Monster Redesigned pellets.
First we have charts for H&N 21 Grain Slugs HP in .217 body diameter.
The top chart shows how the FPS falls as the slugs travel downrange. These numbers are the average of 10 shots using unsorted slugs. As you can see, the velocity falls steadily and predictably the further the slugs travel. Nothing surprising there!
But the second chart shows how the BC value changes with FPS. The BC falls from close to 0.080 at around 940 FPS to around 0.060 at about 970 FPS. And the changes do not run in a straight line, as you can see!
The 30 Yard BC value from this testing was 0.072.
Examples Of Changing BC Values – 23 Grain ZAN Slugs
Here we have the same charts for 23 Grain ZAN slugs.
Again, the top chart shows a predictable, steady fall in FPS as the slugs travel downrange. Again these numbers are the average values from 10 unsorted slugs.
The second chart shows now the BC values are relatively stable until about 860 FPS. Then it falls rapidly.
The 30 Yard BC value from this testing was 0.070.
Examples Of Changing BC Values – 25.3 Grain JSB KnockOut Slugs
In the case of the KnockOuts, the fall in BC out to 50 Yards is really quite small. You could almost say that the change is minimal. But it’s still there – just!
The 30 Yard BC value from this testing was 0.077.
Examples Of Changing BC Values – 25.3 Grain JSB Jumbo Monster Redesigned Pellets
Now we see a difference!
Again the decline in FPS is very steady as the pellets travel downrange. But the change in BC is quite marked, and definitely not straight line.
The 30 Yard BC value from this testing was 0.047. That’s a very high value for .22 caliber pellets!
We’ll have more BC value for slugs data in the next post. Keep tuned for more surprises…
Click here for part two.
Part three is here.