Head’s Up!

How much of an in­flu­ence can mi­nor al­ter­ations in an iden­ti­cal pel­let head de­sign have on ter­mi­nal bal­lis­tic re­sults?

Airgun World - - Contents -

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!

TEST­ING

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!

RE­SULTS

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?

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