Pre-charged pneumatic rifles are incredibly popular today and for many good reasons. A PCP air rifle offers recoilless firing that makes accurate shot placement much easier than it is with spring-piston guns, plus PCPs are close to being silent with the right moderator fitted. Furthermore, many, if not most, are multi-shot too, making them ideal hunting guns.

However, they’re very complex, and in some ways delicate, so you all read the manufacturer’s instruction manuals carefully, didn’t you? “No, actually,” is the most common answer I get to that question. People say “well, it’s obvious, isn’t it?” when I ask how they fill their air reservoirs.

Let me share a few precautionary tales, taken from real-life conversations, to explain just how ‘obvious’ the filling process isn’t. You may well laugh at just how stupid people are, or think that I made these stories up, but I assure you that I did not.

 

Keeping your PCP air rifle clean

I always bang on about keeping all the filling components clean, because inside your PCP air rifle there are many delicate, small parts, including soft little O-rings that keep your precious air inside. If you get grit into the filler and then drive it inside with 200 bar of pressure, that tiny fleck of destruction will set about cutting and gouging anything it can find. The word ‘leak’ comes to mind. Nick just one 5p O-ring, and a leak is what you’ll have. When you go to your gun cabinet and collect the gun that’s been sitting in there for a couple of days, it will be as flat as a pancake and you’ll be looking at a big bill for repairs.

A friend of a friend had an old Logun PCP air rifle and he never kept things clean. Unsurprisingly, the day came and the leaks started, much to his frustration and annoyance. When he found a gunsmith who was prepared to take on such an old and unusual PCP air rifle, he found himself with a quote of over £250 to get it working again. He loved the rifle, so bit the bullet and had the work done, but was upset all the same.

To picture how the damage occurs, imagine taking a handful of sand, dropping it onto the bonnet of your car and then rubbing it in as hard as you could. You can picture just how the paint would look after that, so imagine using 200 bar of pressure behind it and you can easily see how metal could be scratched. And as for soft rubber? Well, it would be cut through in a millisecond.

I write this to ask you please to keep your filling connectors, probes, ports and fittings as near perfectly clean as you possibly can. It will cost you nothing other than a little effort and time, which will be much cheaper than a big gunsmith’s bill. O-rings on probes benefit from the occasional thin smear of silicone grease, but focus on the word ‘little’. This is because dust and grit will stick to them, making a fine grinding paste, and we don’t want that. Apart from that, the only maintenance needed is to clean, clean, clean. Any speck of dust or dirt you can see is your enemy.

Prevention being better than a cure, aim to keep everything clean all the time. I have a plug from Best Fittings that I keep in the end of my filling hose all the time it’s not in use. This is so that my home filling regimen is never going to be a cause of tears.

 

Getting your fill

Next, I keep my filling connectors and probes in a clean box inside the house, not in my workshop, which is frequently full of dusty air. Similarly, my dive bottle lives in the utility room, away from workshop dust and particles. It’s rare indeed that I’ll fill a PCP air rifle anywhere else, apart from when I’m doing long test sessions where multiple fills can be necessary. In that instance, I take a small box for the connectors that’s clean and dry to keep them inside. 

All of the major manufacturers have hundreds of sad tales about people ruining lovely, expensive rifles with dirt, so don’t think that damaging a gun is unusual: it’s not at all. So now we know that hygiene is cheaper than dirt, we need to consider the filling process. 

Before you even think about this, please make sure that you have read the manufacturer’s instructions, and note well the maximum fill pressure. Never exceed this unless you fancy another whopping gunsmith’s bill. You see when the gun fires, a spring drives a hammer forward that knocks a valve open for a moment until the reservoir pressure forces it shut again. If you put too much pressure in the reservoir, the hammer may come knocking, but the valve simply cannot open anymore and your gun is locked up. Off to the gunsmith for you then.

Many people automatically assume that pushing more air in must mean that they’ll get more power out, but they’re 100% wrong. If you even marginally overfill a rifle, the hammer can only open the valve slightly, so you’ll get less power! If you keep firing, eventually you’ll work your way down to the correct pressure where the valve can open fully again and your power will come back up to normal. In fact, some competition shooters intentionally underfill their rifles for better consistency.

Now that you know the pressure you need, attach your connector to the dive tank and open the valve very slowly. You should aim to trickle the air in almost as slowly as you can, and the reason for this is heat. As the air expands, it heats up, and hot air has higher pressure than cold air. Ideally, you’d fill the reservoir to the correct pressure and then set it aside for an hour to cool down. If you then refit the connector, you may find that the pressure has dropped a little and you can top it up. This then maximises the potential stored energy in the rifle. Some filling connectors even have flow restrictors built in to help you with this process.

Let me tell you a couple of true stories about people who ignored these instructions. I once met a farmer at a dinner, and by chance, shooting came up. When I said that I was involved with airguns, he immediately said that he’d bought one of those ‘gas guns’ and that they were rubbish. 

I asked the make and model, to which he answered Air Arms S410. I assured him that he owned a very fine rifle indeed and that something was clearly wrong. After a little digging, he claimed that the pellets were getting stuck in the silencer, which was partly true. You see, he’d filled the reservoir by simply opening the valve fully until it stopped. He’d put 230 bar in a 190-bar gun, and of course the valve was hardly opening at all. When I explained the problem he blamed the manufacturer, but I asked him if he thought putting petrol in his tractor would make it more powerful. Had he read the manual? Not a chance. 

In the opposite way, I heard from a Midlands gunsmith about a certain famous footballer who had bought a top-of-the-line Daystate and then later brought it back because he couldn’t hit anything with it. He claimed that it was totally inaccurate. What had really happened was that he didn’t understand that you had to fill the air up when it ran low. He thought that as long as it went click, it was working. He’d let the reservoir run so low that pellets were getting stuck, one after the other in the barrel, eventually having 36 in there in total! 

Again, he blamed the manufacturer for not ‘addressing the problem’ but we know the truth, don’t we?

So there’s another good lesson. The makers attach gauges for a reason, eh? It only takes a moment to check the gauge and save yourself a whole load of bother and expense. It takes a very long time to unblock a barrel one pellet at a time, and a millionaire footballer might be able to afford that labour charge, but you and I don’t need bills like that. 

It may seem that one filling probe is the same as all the others, but a little look at the photos attached will prove different. I counsel against trying a probe meant for one gun in another, because very high-pressure air should be treated with great caution to avoid injury to yourself and others around you. Used as designed, these systems are perfectly safe, but muck about with them and you could come unstuck.

People like me who have a few guns can really benefit from the quick-change system that’s offered by Best Fittings. This uses a common male adaptor that accepts any probe or coupling and then snaps into the female connector on the tank hose. This means that in seconds you can easily swap from one gun to another with no other tools needed. The company also offers a huge range of filling accessories, and is well worth a look.

I hope that I’ve made you think about the air-filling process a bit more, and that I’ll have helped you to avoid some of the expensive and frustrating pitfalls that await the unaware PCP air rifle owner. They’re wonderful rifles and I seldom use anything else, so I have a well-used system that means that I now don’t even need to think about filling problems at all, and consequently my guns work just as they should.