Gary uses a couple of chronos to gather numerical data from his pellet-testing
Regular readers will already know that I am more than a little obsessed with pellet testing, and in particular the variances we see between calibres and pellet shapes. By conducting tests on terracotta wax last year, and taking cavity moulds with plaster, I was able to demonstrate that given the same pellet shape, the lighter .177 pellets produced a greater wound cavity than the heavier, slower moving .22 pellets. Having established that fact, and in the process upset a few apple carts, I wanted to gain a greater understanding of the physics involved, and to find a way of putting some actual numbers in place of the plaster-cast moulds. So, with the temperatures starting to climb, if only by a little, it was time to break out the terracotta wax and start gathering data.
Although everything I have done so far assures me that .177 leaves a bigger wound track than .22, and therefore promotes the theory that the .177 is giving up more energy, I still had at the back of my head the old belief that the .22 pellet is ‘harder hitting’ than the .177, so I was more than a little nervous that my new experiments might prove me wrong.
I decided to keep things nice and simple for the first of these new tests, so as much as I wanted to get into comparing varying pellet weights, shapes, sizes and distance to target, I decided to compare simple, domed pellets from the same manufacturer; in this case, the Diabolo Field from Air Arms – the .177 and .22 weighing in at 8.4gr and 16gr respectively. The rifles used were the matching pair of Daystate Pulsars used in previous testing, one of which is mine, and the other kindly loaned to me by Terence, at Daystate.
To conduct the tests I fired pellets through a pair of R2a chronographs, supplied by Lloyd, at Blackpool Airguns. I placed a section of the terracotta wax, which I’ve come to rely on for its ability to closely simulate flesh, between the chronos. Simple? Yes, it appears to be, but it’s not as simple as it seems. For starters, how thick do you make the terracotta wax? I had an initial idea that 20mm would be about right, but it needs heating up to 20°C to make it pliable and usable at this temperature,
“I was more than a little nervous that my new experiments might prove me wrong”
although the 20mm thick section wasn’t really capable of supporting its own weight. After further experimentation, I settled on a thickness of 40mm because it was thick enough to support its weight, but wasn’t so thick that it would not be representative of quarry.
The second potential problem was that of particulate dispersion skewing the date. From previous use of the terracotta wax, I was aware that there was a certain amount of ‘splatter’ as the pellet both entered and exited the wax. The entry splash wasn’t an issue because, by definition, the pellet had already passed through the chronograph and been read before entering the wax, so the splatter was secondary to the reading. More of a concern was the spray created as the pellet left the wax. I’d theorised that the spray following the pellet would be moving slightly slower, and that the particles would be too small to be picked up by the second chronograph. I needed to be sure, though,
because if the second chronograph was actually reading the speed of the particles, as opposed to the pellet, my data would be compromised.
After considering both paper and tinfoil as inconvenient splatter catchers, I decided to wrap the second chronograph in Clingfilm to act as a barrier to the many small particles. I then set about testing with and without the Clingfilm to see if there was any variance in the data collected. I was just concluding the testing when my good wife, Marianne, arrived home from work. It’s fair to say that we have some odd conversations in this house, but this pretty much takes the biscuit.
“Hi Honey, I’m home. What have you been up to today?”
“Oh, you know … the usual. Wrapping chronographs in Clingfilm and firing pellets at them through a precisely warmed ballistic clay material to see if particulate dispersion would skew my data. You?” Odd conversations aside, I am happy to say
that although there was a significant amount of particulate dispersion, both forward of and behind the ballistic clay, none of this appeared to impact adversely on the data, so I wouldn’t need to keep wrapping the chronographs in Clingfilm every time I undertook a test firing. Seriously, you have no idea how much of a relief that was! It’s hard enough heating and maintaining several terracotta wax blocks to 20 degrees, never mind having to wrap individually R2a chronographs in cling film for each test shot!
Again, with an eye to keeping things simple at this early stage, I decided to carry out initial testing at around 15 metres. I hoped that
this would prove correct the hypothesis that .177 imparts more energy to the target than .22, and so enable me to move forward in the future by pushing the distance out, and testing varying types of pellet against each other.
A Lincolnshire ‘fret, otherwise known as ‘a thick sea fog’, was moving in so I thought I’d best get a move on with the testing. These frets can get so thick, I swear I’ve seen undead sailors with hooks for hands wandering out of them.
So, what did the day’s testing reveal? First up was the 8.4gr .177 pellet; this passed through the first chronograph at 717fps, registering 9.16 ft.lbs. It then passed through the 40mm-thick ballistic clay and exited the material, passing through the second chronograph, giving readings of 420fps and 3.29 ft.lbs.
Next, it was the turn of the .22 weighing in at 16gr, basically double that of the .177. This pellet passed though the entry chronograph at a slower 543fps with 10.46 ft.lbs., and exited with a speed of 377fps and 5.05 ft.lbs.
If you want to break out the calculators, we can see that the .177 pellet has lost 297fps in velocity as it passed through the target material, and 5.87 ft.lbs. On the other hand, the .22 lost 166fps of speed, and just 5.41ft.lbs.
In simple terms, the .22 arrived with a heck of a lot more energy than the .177, by virtue of its mass, but surrendered less of it to the surrounding ballistic material. Conversely, the .177 pellet arrived much faster, and despite its energy transference, departed having lost less of its velocity to the surroundings.
Despite my initial worries that the data would prove my initial findings wrong, I have been able to show that .177 arrives faster, but with slightly less energy than the .22, but as a result of its lower mass and differing ballistic coefficient, is able to impart more of its energy into the target material as it passes though it, than the heavier, but slower, .22 pellet.
In future articles, I intend to push out the distances and look again at the varying types of pellet on the market. I still have quite a stock of pellets from previous testing and intend to pitch the best of the best against each other. I’ve learned that what you think is going to happen, and what actually happens are two totally different things, and just because I think I know which is the best sort of pellet out there, that doesn’t necessarily mean I’m right. So, if you have a particular favourite, a pellet that you think will dominate the field regardless of calibre, or perhaps one that you think will perform better as a .22 than as a .177, then do please get in touch and let me know. For me, this is a journey, a constant learning cycle, and I’m aware that I have so much more to learn.
How thick should we make the wax samples?
Spring! The time when a young man’s heart turns to thoughts of terracotta wax. The spare tyre on my old Landy made a great rest. With the ‘fret’ moving in from the sea, I knew visibility would soon be limited. Whoops! Good job those guards are there. We’re all human, after all.
My thumb flattened the entry splash, but you get the idea.
Would the ‘splatter’ from the wax skew the data?
Which gives the larger cavity – .177, or .22?
The proof of the pudding is in the eating.