Airgun Hunting Center Cyprus
Terminal Pellet Testing
By Ian Pellant
"Terminal Ballistics" is the study of projectiles impacting various materials. This study was conducted in an endeavor to see what different pellets did upon impact with a "softish" substance. I had read of shooting at bars of "Ivory" soap to test penetration and expansion of pellets, but after shooting at a pack of 4 soap bars, decided that was both expensive and a little messy. Eventually, after prowling around the local home hardware store looking for "ballistic" materials, I stumbled across "Plumber's Putty" - a mixture of limestone, mineral and vegetable oils, talc and clay. It is not as firm as Ballistic Putty, but easier to work with than soap bars.
The results from shooting various pellets into the putty held a couple of surprises:
A few preconceptions about pellet behavior upon impact were disturbed! A most interesting experiment:
The Test Rig:
The test "rig" is easily and cheaply made from:
Two 14oz tubs of Plumber's Putty
40mm cut from a 4" (100mm) PVC water pipe which forms an open ended mold into which the putty is pressed. Retrieving the pellet is simply achieved by pressing from the back of the mold - this opens up the entry hole and the pellet can then be picked out without digging through putty.
A pair of disposable "Painter's" gloves (the putty gets a little messy to handle)
Some pieces of plastic sheet are needed to help level and mold the putty; plus a "splatter" sheet to collect any putty fragments that get blown back by the pellet.
Simply press level the putty into the piece of plastic pipe (or anything suitable you have on hand that is open both sides and can act as a mold / container for the putty). Place the mold on a suitable surface that can absorb any pellet that may happen to fully penetrate the putty, and then shoot into it. All of my tests were conducted by placing the putty mold on a ballistic putty target trap lying flat on the floor; pellets were shot down into the putty. For range shooting, the putty mold can be supported vertically between three nails set into a piece of plywood or similar backing board.
I used the BSA 240 Magnum pistol and the BSA Superstar rifle for the .177 caliber tests. The BSA 240 averages 4.4 foot pounds of muzzle energy, whilst the Superstar averages 14.4 foot pound. Using the 240 Magnum pistol gave results comparable to those of shooting the Superstar over about a 50 yard range without the hassle of actually doing so.
For the .22 caliber tests I used the Webley Hurricane pistol and the BSA Supersport rifle. The Hurricane averages 3.4 foot pounds and the Supersport 14.4 foot pounds with most pellets and an exceptional high average of 15.35 foot pound with Beeman Laser Sport pellets. (A mystery yet to be answered.)
The .177 caliber tests were conducted first and some preliminary conclusions drawn. The .22 caliber tests were then conducted with expectations derived from the earlier tests. Generally, results were in line with expectations in regards to pellet stiffness vs. penetration, but there were a few surprises between the same brand of pellet in the two calibers. They did not always behave the same!
Since the putty was traumatically affected with each shot, and it's temperature may have risen a degree or two during handling, the measured penetrations are only approximate. A truly scientific measurement would have insisted upon an identical homogenous material at a controlled temperature for each shot. My interests were primarily with pellet deformation rather than penetration, so such controls were not enforced.
The photographs show firstly a new pellet, then one shot with 4.4 foot pounds (5.97 J), then one at 14.4 foot pounds (19.52 J):
The photographs show firstly a new pellet, then one shot with 3.4 foot pounds (4.61 J), then one at 14.4 foot pounds (19.52 J):
The most interesting observations are:
These tests also indicate that pellets are designed for airguns of particular power levels. Most air rifles manufactured and sold Europe are built to the UK 12fp non-FAC limit, so many of these pellets were designed for air rifles of 12fp or less. The head separation of the tested hollow point pellets would be less likely to occur with such airguns. The relatively poor velocity / energy results I get with 10.5gr Crosman Premiers in .177, probably indicates that these pellets are designed for more powerful airguns, say 20fp or over. Flat head Match pellets are generally made for rifles of 5fp and are not intended for use in high power hunting guns; but they do have impressive expansion nonetheless at high velocity. It would be nice if pellet manufacturers published the intended energy levels that their pellets were intended for, but having an appreciation of the intended use for a pellet should help you make a selection for a particular airgun. Generally, the heavier pellets in a particular caliber are intended for the most powerful airguns.
It also apparent that pellets of the same brand name, do not always have corresponding behavior in the 2 calibers. The Crosman pellets in particular seem to be softer in .22 than in .177, so their performance both in the barrel and at the target will differ.
As a general conclusion however, it would seem that in either caliber, if the energy level is not high enough to cause significant deformation of the pellet, then it doesn't matter what design the pellet is... they will all penetrate about the same and thus transfer the same amount of energy to the target at the same rate. Only the Beeman Crow Magnum in .177 showed significant deformation at low energy to reduce penetration. The same applies for the .22 caliber Crow Magnum (where the cupped hole expanded - not obvious in the profile photo) and the RWS Super Hollow Point.
At the risk of raising controversy, if asked for hunting pellet recommendations for the BSA spring air rifles, I would suggest the Beeman Silver Bear for general close range work, out to 30 yards, because of it's penetration behavior and the consistent high velocity, energy and accuracy I have achieved with this pellet. For longer range hunting, the Beeman Crow Magnum is a better choice because of its' greater expansion at low energy and higher mass that gives better energy retention over longer ranges. The RWS Super Hollow Point is the more economical pellet (especially if bought from a general purpose sporting mail order house) that offers mid way performance.
Remember that velocity is a function of energy and mass - the heavy (massive) pellet fired from the same gun will initially have the same energy as a much lighter pellet traveling at higher velocity. Over long ranges, the energy loss is greater from less massive pellets traveling at higher velocity. All of these tests were conducted at close range where the velocity varies considerably over the range of pellet weights, but they all carried the same energy. Not exactly "real life" shooting, but it makes comparison much simpler!
An unexpected discovery in this study was the heavy rifling grooves cut into the heads of some of the pellets tested. Checking with my Chrony results I discovered that the energy tests for these pellets was below average for the gun. In the photos you can see the grooving cut into the head off the .177 Crosman Premier and the .22 RWS Super Dome. (And yet the Webley Hurricane deeply cut the skirt of the .22 Super Dome, but not the head!) These pellets yielded lower energy than expected. In the photo of the .22 Laser Sport, the rifling grooves can also be seen, but they are very shallow and uniform compared to the deep grooves cut in the other mentioned pellets. The .22 Laser pellet performs exceptionally well. Is it possible that some pellets are expanding the head in the barrel? Once again, selecting a pellet intended for low power airguns and then shooting it from a much higher power gun may cause problems. Obviously a non-destructive pellet testing rig is required to help study pellet fit... later... perhaps.
Study the photos, draw your own conclusions then buy a sampling of pellets and experiment for yourself. It's cheap fun for the winter indoor season. And, as always, shoot carefully. A high powered air rifle is not a toy.
One final thought:- there have been various speculations as to what inspired the modern airgun pellet "diabolo" shape; my vote goes to the Champagne cork!