Designed by Hugh Earl of Pax Guns, the Piledriver ‘project’ was born out of a desire to make an airgun round that was super-efficient for hunting. In a waisted (or diabolo) pellet, any yaw off its axis while in flight will be corrected via air resistance caused by the skirt – and while that makes waisted airgun ammo very accurate, there is also a downside. Waisted pellets lose energy through drag, partly because of the skirt tipping its edge into the passing airflow, and also because that tail end has a hollow back, creating a partial vacuum. Air tries to rush into this
vacuum with the consequence of drag-inducing turbulence.
Hugh’s solution was to produce a partial boat tail shape at the rear, rather like many rifle bullets have, to improve the efficiency of rear-end airflow. As not many air rifles shoot ammo at supersonic speed, Hugh shaped the Piledriver’s nose as a conventional dome with a flattened peak – and to grip the rifling, it has a modest driving band around the head. Friction in the bore is mitigated by having the surface area of the sides reduced through the use of splines.
These splines also help keep the pellet concentric while in the rifling – important because the loss of a skirt means the Piledriver relies on gyroscopic spin alone to maintain its in-flight accuracy. For this reason, the pellet does need a reasonable velocity to start off with – making it a more suitable choice of ammo for FAC-rated air rifles (as highlighted on the box
Another reason for it being better suited for FAC use is its weight. Made from lead-alloy, a .177 Piledriver (4.46 or 4.50mm head size) tips the scales at a whopping 21 grains – heavier than all but the heaviest of .22 waisted pellets! As for the .22 Piledriver, that’s a meaty 30 grains – and both calibres, being solid, are therefore much better able to take the thrust of air from a high-powered gun than a conventional, hollow-
While such weights may suggest they’re out of the question for use in sub-12ft/lb rifles, it’s worth pointing out that what they lose in velocity, they do actually gain in ballistic efficiency. So they maybe have their place in close-range hunting scenarios, where trajectory isn’t so much an issue, but where maximum stopping power
That said, there is a caveat. Because they fall well outside of the normal weight ranges of .177 and .22 airgun pellets, it is important you check your rifle’s power when using them – especially if you’re intending to shoot Piledrivers through a PCP, which typically work at their most efficient with a heavy pellet. In the case of a 21-grain .177, or 30-grain .22, that might mean a huge swing in muzzle energy for a PCP, taking an otherwise legal sub-12ft/lb rifle over the legal limit. You’re more likely to see a huge downward swing in a spring-powered air rifle, however.
Having tested the Piledriver in an FAC-rated air rifle at the factory, I can vouch that they are impressive performers at high velocities and, subsequently, high muzzle energy outputs. But as I wanted to try the .177 version in my own sub-12ft/lb PCP, the first thing I checked was the power. Thankfully, it did not increase. In fact, it was a tad down, at 10.75ft/lb – probably because the 4.50mm head was quite a tight fit in my Daystate rifle’s barrel.
I decided to limit myself to 25 yards; there’s bound to be a marked trajectory with a 21-grain pellet at sub-11ft/lb and it would be unrealistic to shoot any further out. Of course, accuracy is everything in shooting and overall I found the Piledriver more than satisfactory at my maximum yardage.
A number of test groups were shot over the course of my test sessions and I often found many shots were simply widening the same hole… when suddenly one shot would wander off a fraction and spoil the pattern. Typically I was getting 9mm centre-to-centre at 25 yards – impressive and not too different from the results I obtained from a ‘conventional’ heavyweight diabolo, the 10.65-grain Bisley Magnum. That well-established brand just had the edge in terms of accuracy (5mm c-to-c), though the sub-10mm groups of the Piledriver are still perfectly acceptable. After all, that’s less than half an inch!
Crank the power up, however, and I know from my experience with FAC-powered rifles that the Piledriver will benefit from more gyroscopic spin, with the result that group patterns hold tighter, and for longer.
Due to the massive weight differential between the Bisley Magnum and Piledriver, I thought it would be interesting to compare drop values – and, unsurprisingly, the Piledriver’s parabolic path was 25mm more than the Magnum’s over 25 yards. While that’s not unmanageable in terms of understanding holdover, it’s also a good reason for keeping your shooting ranges short when using them in a sub-12ft/lb rifle.
On the other side of the coin, though, energy retention at the target is where the Piledriver really shines. In my sub-12 Daystate, the .177 Piledrivers still had 9.49ft/lb at 25 yards. Bisley Magnums recorded a muzzle energy a full foot pound more… yet at 25 yards, they’d lost that advantage twice over in terms of stopping power (see Table 1)!
Aside of UK airguns on a ticket, I can think of a number of uses for these niche pellets and many of them lie abroad. A few countries place limits on airguns based around muzzle velocity alone. With a heavier pellet, you can achieve a higher muzzle energy for any given velocity. Some countries restrict airguns to .177 only, so having a super-heavyweight pellet provides more ‘oomph’ opportunity for the diminutive calibre.
UK airgun quarry species generally have an anatomy with thin protection; rabbits, for example, have a delicate skull and soft fur. With perhaps the exception of awkwardly-placed shots on pigeons, where a wing or full crop is involved, there’s marginal use for pellets that deliver shock and awe over and above the norm that’s already out there with ‘conventional’ pellets at sub-12ft/lb. However, a Piledriver fired at FAC velocities would find itself very much at home when used over extended ranges, say out to 60 yards.
Overall, the Piledriver is a very interesting pellet – though I’d say it’s a niche item and very much a round for FAC rifles rather than those at sub-12ft/lb. There will be some loading issues (see panel to the right), but I can still see them as a very useful pellet for the serious hunter to have in his ammo box for when a specific
In PCP guns, the Piledriver really needs to be loaded using a probe below 2.5mm in diameter – one that’s able to fit inside the pellet’s indented base and position it concentric to the bore. My Daystate’s was fine, but Hugh has told me the thicker bolt of a Theoben Rapid is not. Another drawback is that because there’s no waist, these pellets may fall out of some magazines that use an O-ring holding system in their design. In that case, you may be forced to consider a single-shot tray or loader.