How much of an influence can minor alterations in an identical pellet head design have on terminal ballistic results?
Gary Wain experiments with pellet head design. Results are in!
In last month’s article, I looked at .177 pellets of varying weight with differing head shapes. I was surprised to see how well the slightly dimpled hollow point of the Bisley Superfield performed, not only in regard to its terminal ballistic damage, but also when I looked at its quite astonishing accuracy because its grouping size was only fractionally off that of our benchmark, Air Arms Diabolo. The other information harvested from that particular round of testing was that the 8.8gr metal tipped ‘pointy’ pellet, in the form of the H&N Hornet had a tendency to over-penetrate the target material, so it gave up very little of its energy into the clay. This finding corresponded with the results gained last year when simply taking plaster-cast moulds of the cavities as a means of determining ballistic damage. That said, in the back of my mind I seemed to remember that some of the pointy pellets performed particularly well.
I trawled back through my data, and then over a hundred wound cavity plaster moulds to see if I could spark-start any of the ageing grey matter into life, and recalled that there are two types of pointy pellets; those made from a single lead casting, and others that are bi-partite – made up from a main lead casting with a separate tip insert of either plastic or metal. In the case of the Hornets, this insert is metal, and in previous testing, the plastic-tipped pellets seemed to produce better results than those with a metal tip. Why should this be? Was this data repeatable? – and could it be backed up with chronographic data? Well, as they say, ‘There’s only one way to find out’.
I established the H&N Hornet as the benchmark for this round of testing, and then set about finding a plastic-tipped protagonist to pitch it against and after examining the plaster moulds from previous testing, I alighted on the JSB Predator Polymag. This pellet had produced some pretty impressive moulds and I was keen to re-examine it, but despite having a rather impressive plaster cast, I didn’t have any of the actual pellets left. A quick email to Tim at Pellet Perfect remedied this problem, and within a few days I received a delivery of the JSBs, along with quite a few other pellets that will feature in future articles.
There are other pellet test-pack suppliers out there, of course, but I can’t speak too highly of Pellet Perfect. They have a fantastic choice, with consistent stock levels, and should you have any questions, Tim is always glad to answer them and offer guidance and advice, prices are more than
“I seemed to remember that some of the pointy pellets performed particularly well”
competitive and he’s usually the first to get new samples into the UK for trial. So whether you’re into hunting, HFT, match target, or even just a bit of plinking, and are looking for a pellet that suits your needs and matches your airgun, Pellet Perfect are always well worth a look.
I’d previously compared .177 with .22 results, and found that .177 tended to give up more energy and more velocity, so I was keen to see if pellet head shape had any effect on terminal ballistics, and whether or not the previous results would be supported. Theoretically, based on the info I’ve previously gathered, the .177s should produce better results than the .22s, but we’ve had the odd surprise along the way, so this is by no means a given.
RUNNERS AND RIDERS
Down to business then –I’ll be looking at the H&N Hornet in both .177 and .22, and the JSB Predator Polymag in .177 and .22. In
.177, the JSB pellets weigh in at 8.0gr exactly, and the H&Ns are slightly heavier at 8.8gr. When we come to the .22 versions of these pellets, though, it’s strange, but worth noting that they both come in at exactly 16gr. I can’t help getting a little bit excited, and perhaps a tad fizzy in the underpants department, at the thought of matching up two sets of pellets with identical shapes, and identical weights, with no idea which will come out on top – and even more importantly, why. I think I might need to get out more!
As usual, I was testing at approximately 25m, and firing the pellets into a warmed 40mm thick block of terracotta wax, sandwiched between two identical chronographs. I was lucky on this occasion because although it was raining a lot, the wind was mercifully light. Now, when I say it was ‘raining a lot’, I mean, A LOT, and so much that at the other end of the village there was a chap … I forget his name, but he had a job lot of timber and was building a big boat, a very big boat indeed. More worryingly, he had a sign up asking for ‘pairs of animals’. Biblical it was! Biblical, I say!
The images of the terracotta wax speak for themselves, but the numbers are even more important. Firstly, let’s look at the .177 data: In regard to velocity, the H&Ns surrendered 353fps, the JSB giving up a much larger 443fps. When we look at energy, the results are similar; the H&N presented a loss of 6.74 ft.lbs., and the JSBs a more respectable 7.05 ft.lbs.
“it’s apparent that the .177s gave up more velocity than the .22s”
Turning our attention to .22, we can see that the H&N Hornets gave up 263fps as opposed to the JSBs greater 300fps. The energy figures reflect the same pattern; the H&Ns imparted 7.11 ft.lbs. of energy and the JSBs a marginally greater 7.61 ft.lbs.
Having crunched the numbers, it’s apparent that the .177s gave up more velocity than the .22s. The plastic-tipped JSB by far outstripped the metal-tipped Hornets, 443fps vs 263fps. The energy tables become slightly less stable because the .22s appear to have the advantage; the H&N Hornet .177 gave 6.74 ft.lbs., and the .22 a figure of 7.11 ft.lbs. These results are similarly reflected in the JSB data, the .177s giving a reduction of 7.05 ft. lbs., and the .22s a a staggering 7.61ft.lbs., which is one of the largest energy losses we have seen to date.
IT’S ALL IN THE HEAD!
So what are we to make of this? I had a sneaking suspicion that the secret would lie within the design of the pellet heads, and proof would require the careful application of snipe-nosed pliers, tweezers, and a great deal of patience. I ripped off metal or plastic tips from the lead encasements to examine the intricacies of their designs and for starters, I found that the metal tips of the H&Ns, quite loose in their lead sockets, are actually much harder to remove than the plastic tips of the JSBs, which came away really easily. Upon removal of the tips I was able to get a better view of the ‘socket’ – this is the bit that expands when the tip comes away on impact, essentially turning the pellet into a hollow point. I found that the JSBs have a wider socket with thinner walls, which is much more likely to compress and expand than the thicker walled socket of the H&N. So, if we combine a head that’s less likely to break away on impact, with a cavity that’s not capable of as much expansion, you have the answer to why the JSBs surrendered more of their energy and velocity into the target material. If we want to know why the .22s out-performed the .177s, then we have to look back at what we know about coefficient of form and terminal ballistics. The .177 has a better external ballistic coefficient during its trajectory, so its smaller frontal surface and proportionately thicker socket walls cause it to expand less on impact than the .22.
Like I say, it’s all in the head.I
It was tipping it down so I had to find a way of protecting the test equipment. They say that necessity is the mother of invention.
Will the metal-tipped H&Ns or the plastic-tipped JSBs perform best?
I’m testing both .22 and .177, so I’ll need both of the Pulsars today.
When cold, just 20mm of the terracotta wax will stop any pellet dead in its tracks.
The .177 exit wounds. Which would please you most?
Plenty more testing to come.
The JSB (left) has a shallower hollow with thinner side walls. Will it do better than the H&N?
Holy Moly! Which pellet did this?