Mark Camoccio discusses the pros and cons of high-power delivery
PRE-CHARGED PNEUMATIC (PCP)
Whilst immensely powerful, pre- charged pneumatics utilising fantastic brass ‘ ball reservoirs’ were actually used in the Napoleonic Wars, the modern pre- charged pneumatic (PCP) has Daystate to thank, from the 1970s, as recognised pioneers of the system in the modern age. The precharged pneumatic sees the rifle built with an on-board reservoir to hold highly compressed air. This cylinder needs to be connected to an external power source, be that a dedicated airgun pump, or a diver’s bottle, and then charged to a prescribed pressure, normally somewhere between 130-250bar. Once fully charged, the shooter will then have an air supply, good for a certain amount of shots, which can vary dramatically dependent upon the gun’s design. Conventionally-styled PCPs following the configuration of straight cylinder underneath the barrel, typically offer 50-80 shots dependent upon the model. So- called ‘ buddy bottle’ designs, where a large, exposed, gun-mounted air bottle sits at the front of the action, can offer far greater shot counts, in the region of 200- 600 shots.
With PCPs, we then have the issue of non-regulated or regulated action. Many shooters, particularly competition shooters, can get hung up on consistency, and for peace of mind, a regulated action can be the way to go. The regulator effectively meters a precise amount of air for each shot – occasionally, with the use of a separate, small inner chamber within the cylinder. Consistency should be improved, and with it downrange performance, due to the flatter power curve over the full charge. With a standard pre- charged action, what’s called a ‘ knockopen valve’ is normally utilised, and here the hammer knocks open the valve for each shot. As the pressure in the main cylinder slowly decreases, it becomes easier for the hammer to knock open the valve, so a slightly different pulse of air might be released over time. This can cause quite a marked ‘power curve’, which is when the velocity rises and falls.
With this style of airgun, it is vital to monitor carefully the pressure to which the gun is charged, and research so that you know which particular action likes a certain fill pressure. Charge an initial fill pressure too great, and the hammer can come up against more resistance from the valve at the start, causing lower velocities, settle into the smoother, flatter part of the charge (commonly known as the ‘sweet spot’), and then as the residual air pressure drops, so finally, will the velocities. There are no such concerns over the fill pressure with a regulated action, and for this reason, many shooters put great store by paying a premium for a fitted regulator. Many manufacturers offer non-regulated and regulated models, but precision regulators can also be purchased as after-market add- ons, from such specialist outlets as Airmasters, who are highly regarded within the industry. With a ‘ reg’ fitted, shot count would normally increase too.
The upside of PCPs is easy loading by just pulling back a small bolt or lever, and of course, recoilless shooting because the gun hardly moves on firing. The downside is the gun’s reliance on that external power source, a pump or diver’s bottle, and the initial cost of that charging gear.
To my mind, the single-stroke pneumatic is the holy grail of airguns, but whilst the system has proven successful for pistols, designers have still struggled to achieve full power in .177 calibre, certainly in production models. The design sees a large lever mounted on the rifle, that needs to be pulled all the way back. On the outward stroke, air is sucked into an internal chamber. On the return stroke, that air is compressed. That volume of pre-compressed air then powers the pellet. A consistent cocking stroke is needed to keep the volume of air the same each time, but with care, velocities with this style of gun can be phenomenally consistent. Recoilless shooting is the prize, but these guns are inevitably heavy.
American manufacturers were always keen on this style of gun, with Benjamin and Sheridan perhaps the best known. Here, an on- board pumping system allows for between 3 and 10 pumps to be completed to achieve full power, with a blow- off valve normally in place to keep everything legal. Again, this style of airgun offers recoilless shooting, and can be fairly light, but the downside is the effort required to complete those last few pumps. Popular in the late ‘ 70s and ‘ 80s, this style of gun isn’t often available in the UK, presumably due to lack of demand.
So as we can see, there’s an incredible selection of hardware out there! Next month, we’ll look at choosing the right model for the right application.
“The regulator effectively meters a precise amount of air for each shot”
The modern PCP is a superb tool, and easier to shoot than some other types
Multi- pumps need a fair bit of input effort
Don’t forget, charging gear is needed for a precharged airgun
The FX Independent is unique
A bolt action is the most common type of PCP
A typical filling valve connector on a PCP