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What is the difference between a regulated PCP and an unregged one?

by Nigel Allen

Precharged pneumatic (PCP) air rifles are powered by compressed air contained in either an integral air cylinder or buddy-bottle. Although the PCP is the serious airgun shooter’s choice, its concept is inherently simple: a hammer strikes a valve which releases some air to thrust the pellet out of the barrel. The hammer always strikes with the same force, so the amount of air released by the opening valve changes as the rifle’s on-board air pressure behind it drops. This affects the velocity (power) output of the rifle as it progresses through its air charge, resulting in what’s known as a power curve.

The specific shape of the power curve varies according to the rifle’s design. Generally, an unregulated PCP’s power output will rise to a peak before dropping off to the point it needs recharging. A power output that’s dependent on the air rifle’s pressure is not ideal because the pellet’s downrange point of impact (POI) will alter accordingly. Because of this, many airgunmakers incorporate an air regulator into their guns. In a regulated PCP, the power output stays consistent throughout its entire air charge.

Comparison of typical power outputs from a regulated and non-regulated precharged pneumatic air rifle

So, which to choose? Although a regulated PCP may seem the ideal, unregged PCPs have been around for many years and are still popular. Indeed, much R&D has been undertaken in the PCP world, so the simple ‘knock-open’ valve of old is a far cry from what we see on today’s airgun hardware. The Slingshot hammer/valve set-up used in the unregulated Daystate PCPs is one such example of how far unregged PCP design has evolved. Nevertheless, characteristics of unregged and regged systems are an important consideration when choosing a PCP for your specific shooting needs.

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Between the first and last shots of an unregged PCP’s charge of air – its ‘usable’ range – the output will follow a power curve, peaking somewhere around the mid-point of the curve. While the duration of the peak depends solely on the rifle’s inherent design, this part of the curve is referred to as the ‘sweet spot’. It’s where the shot-to-shot consistency – and so the rifle’s accuracy – will be at its best. The longer the sweet spot, the better. Ideally, that is where you want to be doing most of your shooting (and where you should zero your scope).

Of course, you can shoot either side of the sweet spot, but you may well see a slight change in the pellets’ POI. At relatively close ranges this probably isn’t a problem, but it may shift your pellets outside acceptable limits for hunting or competitive target shooting at longer distances. Therefore, with any unregulated PCP, it pays to familiarise yourself with the characteristics of its power curve so that you can compensate for POI shift if required.

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Although an unregged PCP lets you shoot throughout its usable pressure range (200 down to 100 BAR in this example), the best consistency, power and accuracy will be obtained by shooting in its ‘sweet spot’ (165 down to 120 BAR in this example)

For example, your rifle may fill to 200 BAR and then, 150 shots later, need a refill at 100 BAR. Let’s assume its sweet spot spans 65 of those 150 shots. Then it would be worth noting on the rifle’s manometer what pressure range relates to that 65-shot section – perhaps between 165 and 120 BAR. If the number of shots you get per charge of air doesn’t bother you, you could choose to fill the rifle only to 165 BAR each time, and always refill it at 120 BAR. Yes, the trade-off is that you’d be reducing the rifle’s shot-count, but in return you’d be getting an output performance on a par with a regged PCP. Plus, by starting at lower pressures, charging the rifle from a manual pump will be less effort, and you’ll get longer periods between scuba tank fill-ups.

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Where an air regulator is fitted to a PCP, air release is far more controlled for the entirety of the rifle’s charge and there is therefore no power curve. Effectively, a regulateded PCP offers a sweet spot that extends from the first to the last shots of the usable shot range. In some cases, because a regulator deals with air delivery more efficiently, the rifle also returns more shots between fill-ups.

Generally, a regulator system incorporates a secondary air chamber (the plenum chamber) which is designed to operate at a constant pressure. This means that as the rifle’s air pressure drops, the main firing valve always delivers an exactly-metered volume/pressure of air. The benefit of this is that the rifle’s power output is the same, no matter where it is within its charge cycle.

That said, it is important not to let the pressure in the rifle’s main air reservoir drop below that of the regulator’s operating pressure, else the regulator effectively becomes redundant in the air flow chain. Many gunmakers now incorporate an additional gauge on their regged PCPs to specifically indicate the regulator status, like on the Brocock Commander PCP.

The regulated Brocock Commander has two manometers – one for its HUMA regulator’s fixed pressure (top) and one to show the pressure status of the rifle’s main air reservoir

While ‘managing’ the power curve of an unregged PCP isn’t exactly a headache for most shooters, there’s no denying that the fill-and-forget operation of a regulated PCP is more straightforward. However, regulated PCPs cost more than their unregged counterparts, so you have to weigh up their worth in your particular scenario.

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FT, HFT and benchrest competition shooters, who seek ultimate precision in every aspect of their sport, may be able to justify the outlay for a regged PCP, but for everyday shooting/hunting assignments, a good quality, unregged PCP is equally as good if you have a full understanding of its power curve.

Yet never dismiss the addition of a PCP regulator as ‘just another thing to go wrong’. That may have been the case when airgunsmiths were experimenting with them many decades ago. But just like knock-open systems have evolved, the PCP regulator has also graduated. Specialist regulator manufacturers have risen to the forefront of the airgun industry, with many gunmakers incorporating their proven designs in their regulated PCP. Daystate, for instance, have partnered with the world renowned HUMA to develop a metering system in the new regulated HR Huntsman Regal, Renegade HR and Wolverine R air rifles.

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Ethan Smith is a seasoned marine veteran, professional blogger, witty and edgy writer, and an avid hunter. He spent a great deal of his childhood years around the Apache-Sitgreaves National Forest in Arizona. Watching active hunters practise their craft initiated him into the world of hunting and rubrics of outdoor life. He also honed his writing skills by sharing his outdoor experiences with fellow schoolmates through their high school’s magazine. Further along the way, the US Marine Corps got wind of his excellent combination of skills and sought to put them into good use by employing him as a combat correspondent. He now shares his income from this prestigious job with his wife and one kid. Read more >>