PCP With Nitrogen Charge

[ani-m]

Please do not confuse nitrogen with CO2. Nitrogen at 200 bar offers no measurable advantage over compressed air in PCP air rifles.

Therefore, it is practically never used in target shooting.

For the projectile, it makes absolutely no difference whether the pressure comes from compressed air or pure nitrogen.

Both gases have virtually identical density, the same speed of sound, and the same flow characteristics at the pressures relevant to PCP.

Muzzle velocity, consistency, energy – all the same.

The only real difference lies in moisture and corrosion.

Compressed air can contain residual moisture, especially with poor-quality compressors.

Nitrogen is always dry. No corrosion because there is no oxygen = no oxidation.

However, modern PCP compressors already deliver extremely dry air.

In practice, therefore, no advantage is measurable.

This may have been an argument 30–40 years ago, but not anymore.

The O-rings, valves, and regulators are designed for air.

Nitrogen is not "gentler."

Therefore, there is no difference in aging or leakage.

It is sometimes claimed that nitrogen runs more stably in the regulator. But this is physically incorrect. The pressure-temperature characteristic curve is practically identical. No reduced pressure drift. No advantage in shot-to-shot consistency.

There is also no safety benefit:

200 bar remains 200 bar.

It's different with CO2.

CO2 exists in the cartridge in both liquid and gaseous states. The pressure is determined solely by the temperature.

0°C -> 35 bar up to 50°C -> 130 bar

CO2 cannot be "simply stored in gaseous form" at 200 bar like air or nitrogen.

At 200 bar, CO2 is necessarily liquid or supercritical.

Therefore, CO2 is unsuitable as a "normal propellant gas" for PCP.

CO2 has very low critical values.

Temperature 31.0 °C / Critical pressure 73.8 bar

Of course, nitrogen can also be liquefied. But see for yourself:
Nitrogen critical temperature: −146.9 °C / critical pressure: ~33.5 bar
At room temperature, nitrogen is far, far above its critical temperature; it remains a true gas even at 200 or 300 bar. CO₂, on the other hand, does not.

N₂O (nitrous oxide) is a different story altogether. For N2O, as with CO2, temperature is the decisive factor for pressure.

 

[woody b]

Filling the gun with nos will make my accuracy even more laughable......

 

[Hollowlegs]

Where are these deep-sea watch helium filling stations based?

In the diving bell, the air breathing mixture is higher in helium and this can get through the seals on the watch, expands as the pressure decreases on the way up and boom

 

[Marky807]

Apart from being bummed by Mr Big while doing stir? Probably none.

The problem is the next numpty who sees it’s ok to use nitrogen who then takes the next logical step: it’s ok to use oxygen.

If we keep to “Breathing air only” all this dumbfuckery is avoided

I fully understand its illegal

 

[Cannon Fodder]

Let's just stick with one bit of our shooting set up being filled with nitrogen. No need for it to be in more than one.

 

[Fivla]

I used to work with nitrogen a lot. We used it for purging equipment, pipework and vessels of explosive atmospheres, and for pressure testing. Nitrogen is an inert gas and is non toxic but it can also displace the oxygen in the atmosphere, especially in an enclosed space.
one breath of it can render you unconscious and if you arent removed from it you would very quickly die. Ive heard of a few stories about people entering an enclosed space filled with nitrogen and dying, and their mate then going in to help them and also being overcome.
If the general public were to start keeping N2 at home, storing it in sheds or garages id bet there would be regular reports of them dying due to a small leak in an enclosed space.

 

[Marky807]

I used to work with nitrogen a lot. We used it for purging equipment, pipework and vessels of explosive atmospheres, and for pressure testing. Nitrogen is an inert gas and is non toxic but it can also displace the oxygen in the atmosphere, especially in an enclosed space.
one breath of it can render you unconscious and if you arent removed from it you would very quickly die. Ive heard of a few stories about people entering an enclosed space filled with nitrogen and dying, and their mate then going in to help them and also being overcome.
If the general public were to start keeping N2 at home, storing it in sheds or garages id bet there would be regular reports of them dying due to a small leak in an enclosed space.

Now thats a good point

 

[Battery]

The reason why not has been given above, it's illegal.

I wasn't really commenting on the legality of using Nitrogen. From a technical stand point it makes good sense, possibly safer than air

 

[ani-m]

Helium molecules are very small so would leak way more than air, that’s why very deep sea divers watches have an helium escape valve so when they come up and decompress their watches don’t blow apart

Okay, the sense or nonsense of using helium as a propellant for PCP.

In the USA (I don't know if it's done in other countries),

it's actually being done—helium instead of compressed air.

Mostly experimentally or "just for fun."

But precisely because it's being done, it's also very clear why it hasn't caught on.

Okay, PCPs with helium instead of air, focusing on extremely high muzzle velocities ("Supersonic Airgun").

I consider this a gimmick; those more interested in chronograph numbers than precision.

Helium can generate higher muzzle velocities because it has a very high speed of sound.

(Speed of sound in helium is approximately 1000 m/s, in air approximately 343 m/s).

There's faster pressure equalization.

Nevertheless, I consider it nonsense (for anything other than fun).

Because the precision is poor.

In practice, everyone who has seriously tested it reports significant fluctuations in muzzle velocity, resulting in poorer shot groups. The shot is extremely sensitive to valve timing.

In my opinion, this makes it completely unusable for FT/HFT/BR.

The biggest practical problem has already been mentioned.

Helium diffuses through O-rings, plastics, and even metal (albeit slowly and measurably only with sensitive methods. I wanted to mention it nonetheless).

Pressure loss overnight. Regulator (If one is used.)"empty," even though nothing is broken.

This isn't a defect—that's helium.

Modifications are therefore necessary.

For it to work halfway decently, a higher gas volume per shot is needed. This means larger transfer ports, different valve springs, different opening times, and ideally, no regulator at all.

I think it's okay for a hobby experiment.

Completely absurd for everyday use.

 

[Gummage]

It's illegal, impractical, and why chase power when our rifles our restricted to 12 ftlbs, and achieve that with ease...

 

[Quentyn]

I had a thought today and wondered what would happen if a PCP air gun was charged with nitrogen. I copied and pasted this from Google. It surprised me and now I wonder if it would benefit a competition shooter would benefit?

If a PCP (Pre-Charged Pneumatic) air gun was charged with nitrogen, it would operate with no issues and the results would be virtually the same as using compressed air. The gun would function safely and likely experience some minor benefits to its internal components due to the properties of nitrogen.

Key Outcomes

• Safety: Nitrogen is an inert gas and makes up about 78% of the air we breathe. Unlike oxygen, it does not support combustion, so there is no fire or explosion risk, even if oil or other contaminants are present in the air gun's system. This makes it a very safe alternative to regular air.
• Performance: There would be no noticeable performance difference in terms of pellet velocity or consistency for a standard air gun. The physical properties of nitrogen gas at typical air gun pressures are very similar to those of air.
• Benefits to the Gun: The primary advantage of using pure nitrogen is that it is very clean and dry (moisture-free). This eliminates the moisture that is present in compressed air (even filtered air), which in the long term helps prevent internal corrosion (rust) and the degradation of O-rings and seals. The larger nitrogen molecules may also result in less leakage past seals compared to air.
• Potential Drawbacks: The main reasons most people do not use pure nitrogen are the added cost and reduced availability of high-pressure nitrogen tanks compared to sourcing high-pressure breathing air. Some manufacturers might also void the warranty if a gas other than air is used, primarily to avoid liability issues from users experimenting with dangerous gases like pure oxygen.

If you want to bit of a laugh go on to the other forum and suggest that people use pure nitrogen..

Given that you breathe over 75% nitrogen as you're currently sitting there reading this message there's no problem at all and filling your gun with nitrogen.

Pure oxygen on the other hand... I saw a picture of a theoben that has been filled with pure oxygen and the block was in many different pieces.

 

[zakdingel]

There is clue in the Name AIR gun----not gas gun they are what farmers put in fields ---stick with air lads and keep safe as possible--unless it's a gas ram but then that sealed in a tube like you get on your car boot

 

[Hollowlegs]

Please do not confuse nitrogen with CO2. Nitrogen at 200 bar offers no measurable advantage over compressed air in PCP air rifles.

Therefore, it is practically never used in target shooting.

For the projectile, it makes absolutely no difference whether the pressure comes from compressed air or pure nitrogen.

Both gases have virtually identical density, the same speed of sound, and the same flow characteristics at the pressures relevant to PCP.

Muzzle velocity, consistency, energy – all the same.

The only real difference lies in moisture and corrosion.

Compressed air can contain residual moisture, especially with poor-quality compressors.

Nitrogen is always dry. No corrosion because there is no oxygen = no oxidation.

However, modern PCP compressors already deliver extremely dry air.

In practice, therefore, no advantage is measurable.

This may have been an argument 30–40 years ago, but not anymore.

The O-rings, valves, and regulators are designed for air.

Nitrogen is not "gentler."

Therefore, there is no difference in aging or leakage.

It is sometimes claimed that nitrogen runs more stably in the regulator. But this is physically incorrect. The pressure-temperature characteristic curve is practically identical. No reduced pressure drift. No advantage in shot-to-shot consistency.

There is also no safety benefit:

200 bar remains 200 bar.

It's different with CO2.

CO2 exists in the cartridge in both liquid and gaseous states. The pressure is determined solely by the temperature.

0°C -> 35 bar up to 50°C -> 130 bar

CO2 cannot be "simply stored in gaseous form" at 200 bar like air or nitrogen.

At 200 bar, CO2 is necessarily liquid or supercritical.

Therefore, CO2 is unsuitable as a "normal propellant gas" for PCP.

CO2 has very low critical values.

Temperature 31.0 °C / Critical pressure 73.8 bar

Of course, nitrogen can also be liquefied. But see for yourself:
Nitrogen critical temperature: −146.9 °C / critical pressure: ~33.5 bar
At room temperature, nitrogen is far, far above its critical temperature; it remains a true gas even at 200 or 300 bar. CO₂, on the other hand, does not.

N₂O (nitrous oxide) is a different story altogether. For N2O, as with CO2, temperature is the decisive factor for pressure.

I think the nitrogen molecules are larger so the risk of leaks is reduced, another reason they use it in tyres?

 

[Tinbum]

If you want to bit of a laugh go on to the other forum and suggest that people use pure nitrogen..

Given that you breathe over 75% nitrogen as you're currently sitting there reading this message there's no problem at all and filling your gun with nitrogen.

Pure oxygen on the other hand... I saw a picture of a theoben that has been filled with pure oxygen and the block was in many different pieces.

Which is why we should stick to the credo of breathing air only

 

[zakdingel]

I think the nitrogen molecules are larger so the risk of leaks is reduced, another reason they use it in tyres?

I think it is lighter than air and dose not get effected as much by heat whilst under racing conditions so gives you less rolling resistance so your engine works under less strain

 

[Tinbum]

I think it is lighter than air and dose not get effected as much by heat whilst under racing conditions so gives you less rolling resistance so your engine works under less strain

A molecular weight of 15 as opposed to oxygen’s 16, hence breathing becoming harder as you gain altitude

 

[chouchin66]

There is printed, tested & accepted wisdom contained in powder cartridge reloading manuals, a good few folks think they can build a " better mousetrap" by exceeding safe & published data, not heeding warnings... Usually they end up with shrapnel embedded, eating a bolt, & then requiring some reconstructive surgery...or an undertaker. If you wish to re write the standard operating manuals, fine ! If you lose body parts or gain a harp by doing so, don't say you weren't warned...go ahead, get your Darwin award - there's more than enough idiots to take your place !

 

[ani-m]

I think the nitrogen molecules are larger so the risk of leaks is reduced, another reason they use it in tyres?

Yes, that would be a plausible reason.

But here too, we need to look at the realities.

Regular air loses about 1–2% pressure per month.

Nitrogen loses about 0.5–1% per month.

This applies to car tires, of course.

Since compressed air (except at Aral) is still free at many gas stations and service centers, it's purely a matter of cost-effectiveness whether you fill car tires with nitrogen or regular air.

I consider it pure marketing.

Oxidation is real, but slow. The oxygen content in the air can age rubber, slightly corrode steel cords, and valves/rims can oxidize. But modern tires are designed for this. Aging due to UV radiation, heat, flexing, and general use is significantly greater.

Furthermore, nitrogen in the tire offers no protection against these external factors.

The real difference is often the compressed air (I mean standard workshop compressors). This usually contains water vapor. Water in the tire amplifies pressure fluctuations with temperature and can, of course, also promote corrosion.
Dry air would be almost as good as nitrogen.

Unfortunately, you have no control over the quality of the air.

Therefore, I'll be honest and say that nitrogen in the tire can be an optimization of an already good system.

But it's not a game-changer.

With air rifles, these factors are even less significant.

If you fill up with high-quality compressed air, you'll hardly have any problems with corrosion caused by the compressed air. Use in unfavorable climatic conditions will play a bigger role.

If the system is airtight, you'll hardly have less leakage with nitrogen than with compressed air. At least not if the rifle isn't just sitting in a corner.

 

[Bighit]

I used to work with nitrogen a lot. We used it for purging equipment, pipework and vessels of explosive atmospheres, and for pressure testing. Nitrogen is an inert gas and is non toxic but it can also displace the oxygen in the atmosphere, especially in an enclosed space.
one breath of it can render you unconscious and if you arent removed from it you would very quickly die. Ive heard of a few stories about people entering an enclosed space filled with nitrogen and dying, and their mate then going in to help them and also being overcome.
If the general public were to start keeping N2 at home, storing it in sheds or garages id bet there would be regular reports of them dying due to a small leak in an enclosed space.

we used it to test pressure valves and i was asked to test and adjust around 20 of them and the test consisted of two rounds of blowing Nitrogen threw then to test them then the same again is they had to be adjusted . The room had a door but the top of the walls were open to the outside air .

I started feeling the effects of it and had to stop and go outside the room .

The door was removed and exhaust fans fitted to keep the air flowing when test the pressure valves.

 

[xlucine]

I used to work with nitrogen a lot. We used it for purging equipment, pipework and vessels of explosive atmospheres, and for pressure testing. Nitrogen is an inert gas and is non toxic but it can also displace the oxygen in the atmosphere, especially in an enclosed space.
one breath of it can render you unconscious and if you arent removed from it you would very quickly die. Ive heard of a few stories about people entering an enclosed space filled with nitrogen and dying, and their mate then going in to help them and also being overcome.
If the general public were to start keeping N2 at home, storing it in sheds or garages id bet there would be regular reports of them dying due to a small leak in an enclosed space.

CO2 can do the same, of course. It's not uncommon for someone to get a surprise when they check on the dry ice they stored in a cupboard