This month Neil Price talks us through pre-charged pneu­matic cylin­der pres­sure

Air Gunner - - Contents -

Neil Price ex­plains the safety as­pects of PCP cylin­der pres­sure, and how to take ba­sic pre­cau­tions

Any air-pres­sured ves­sel can be ex­tremely dan­ger­ous if not treated in the cor­rect man­ner. They are ba­si­cally pipe bombs that can ex­plode when mis­treated, so the great­est care must be taken when do­ing any­thing with a pre- charged pneu­matic gun’s air pres­sure cylin­der.

The first and most im­por­tant thing is the fill pres­sure. Most cylin­ders have it stamped on them, and hand­books state cat­e­gor­i­cally that the MAX­I­MUM fill pres­sure is 200 bar on many guns, although this does vary from man­u­fac­turer to man­u­fac­turer. That is al­most 3000 pounds per square inch of pres­sure. Now then, as stated, that is a max­i­mum fill pres­sure, it is not a tar­get pres­sure that you have to achieve, ex­actly the same as speed lim­its on our roads. It is a fig­ure that you are al­lowed to go up to, but not go over.

When fill­ing pre- charged pneu­matic air­gun cylin­ders, al­ways go on the pres­sure in­di­cated gauge on the high-pres­sure tank that you are fill­ing from. Th­ese are usu­ally much more ac­cu­rate than the small manome­ters that are fit­ted to air­guns.

I have found that when filled to the max­i­mum pres­sure, guns are not as ac­cu­rate as they should be un­til the pres­sure in the air cylin­der has dropped by about 20 bar, so I only fill my guns to 180 bar and I find that the ac­cu­racy is there for me from the first shot.

In the past, I had a ri­fle brought to me, which was ‘ leak­ing’. It was an Air Arms S400 and as I ex­am­ined it, I found that one end of the air cylin­der was like the bot­tom of a bell with the whole pe­riph­ery blown out. The owner swore black was white to me that he had never filled it over 200 bar. Need­less to say, I ac­cepted that state­ment with a large pinch of salt.

It is very im­por­tant that you only fill the air cylin­der of an air­gun with clean, dry com­pressed air. NO OTHER GASES ARE EVER TO BE USED. Us­ing other gases has caused ac­ci­dents in the past that have led to some nasty in­juries, so please heed this warn­ing.


When fit­ting the adap­tors into the neck valve of your 300 bar air tank, never use a span­ner to tighten them into the alu­minium threads. This is for two rea­sons; the ex­cess force that can be ap­plied with a span­ner can dam­age the alu­minium threads in the valve, and the ‘O’ ring on the seal­ing face will be­come com­pletely flat­tened and its work­ing life will be vastly short­ened. Al­ways tighten th­ese into the valve by hand only, and then let the com­pres­sion on the ‘O’ rings do the work. Also, reg­u­larly check the con­di­tion of the ‘O’ rings on the tank con­nec­tor and the fill probes. If you have more than one pre- charged pneu­matic gun that uses dif­fer­ent fill probes, then a ver­sa­tile fill sys­tem should be thought about. A very good source of th­ese prod­ucts is Best Fit­tings, a com­pany that spe­cialises in fill­ing ac­ces­sories for air­guns and can be found at https://www. best­fit­

When fill­ing an air cylin­der, al­ways fill it as slowly as pos­si­ble so then it will be easy to stop the fill at the pre­cise re­quired pres­sure, and so min­imise the danger of over-fill­ing. Most air tanks are now fit­ted with slow-re­lease valves any­way, but some older tanks that you might buy sec­ond- or third-hand can have just open and shut valves. This means that the full tank pres­sure can be put into the air cylin­der in a frac­tion of a sec­ond. That is why the fill knob should only be turned very slowly and under com­plete con­trol, so that the air is trans­ferred to the gun’s cylin­der at a very slow rate. If a cylin­der is ac­ci­den­tally over-filled, then dry fire the gun un­til the safe work­ing pres­sure or below has been reached.


At the other end of the scale, do not let the pres­sure drop too low in the air cylin­der. The most ac­cepted min­i­mum pres­sure for re­fill­ing is when 100 bar is reached, and no lower. For one thing, with too low an air pres­sure in the gun, ac­cu­racy suf­fers greatly, and se­condly, pel­lets might not come out of the end of the bar­rel. If one gets stuck in the bar­rel then that usu­ally can eas­ily be cleared, but if the shooter does not re­alise that a pel­let did not leave the bar­rel, then fur­ther shots might be taken get­ting more and more pel­lets stuck. The worst one that I have ever seen is when there were over 20 pel­lets stuck in a bar­rel. The only way to re­move them was to melt them out with a gas torch on the out­side of the bar­rel. The les­son here is to keep an eye on the gun’s pres­sure gauge, or be aware of the num­ber of shots you have taken.

“that is a max­i­mum fill pres­sure, it is not a tar­get pres­sure that you have to achieve”

The gauge on your dive bot­tle will be more ac­cu­rate than the one on the gun The max­i­mum fill pres­sure is of­ten writ­ten on the reser­voir

Only ever use clean dry air in your PCP

This con­nec­tion only needs to be hand-tight

If the pres­sure gets too low, pel­lets can get stuck in the bar­rel

Re­place any ‘O’ rings that show signs of wear

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