Before using a lubricant, read the sections below that relate to the application you are using it for. Lubricants containing petroleum distillates (hydrocarbon solvents) or other flammable substances are not generally safe. They can end up in places where they won't evaporate before the gun is charged or fired. Combustion or explosion could result. WD40, many gun oils, cleaning solvents, silicone sprays and most similar products contain flammable chemicals. Products intended for firearms are not generally safe for airguns. Substances with any significant toxicity should not be used. Not only could this be harmful with regular contact but these can become aerosolized and inhaled while charging or firing. Which lubricants are safe is explained below. Section 1 covers low-pressure CO2 and self-contained pump models. Section 2 covers high-pressure break barrel, PCP and HPA guns.
SECTION 1 : CO2 & SELF-CONTAINED PUMP
Crosman suggests Pellgunoil which works great in moderate temperatures and comes in a convenient applicator tube. It's expensive to use if you do a lot of shooting. As a less expensive alternative any SAE 30 or 10W30 engine oil will work very well.
It's a myth you shouldn't use petroleum oil for airguns. This myth stems from the common misconception that petroleum distillates and oil are the same thing. They are not, oil is what's left after the distillates are removed from crude oil. This subject is confusing to many because some distillates are commonly referred to as oil. The most common examples are heating oil and penetrating oil which are both petroleum distillates. The oil that is safe is called mineral oil also known as heavy oil. Mineral oil is not toxic or flammable. It protects against wear and corrosion better than silicone or natural oils, will not harden and doesn't become rancid. This is why all engine oils, including synthetics, are mineral oil based. It will not hurt the seals in your gun. Modern airgun seals are made of materials like Nitrile and urethane which are engineered for use with petroleum oils. I've been using engine oil in airguns for many years and have never seen a modern o-ring swell or dissolve.
It's a myth that engine oil is toxic, most are not. Some do contain potentially harmful additives, these will say so on the bottle and should be avoided. Used engine oil is more toxic and combustible, this is due to contaminants from fuel, combustion and wear.
It's a myth you shouldn't use detergent oil for an airgun. It actually works better than non-detergent. It has wear and corrosion inhibiting additives and helps remove moisture and contaminants as it works it's way through. An airgun doesn't experience the type of action or gain enough moisture for emulsion to be an issue.
Crosman Pellgunoil (Monolec GFS 8430) is SAE 30 engine oil with a high level of detergency. Because it is single viscosity it gets significantly thicker in cold temps. 10W30 works better when cold, especially in self-contained pump guns. In extreme cold lower viscosity may work better. In hot temps a thicker oil may be preferred.
The links below contain more information about Pellgunoil and other Crosman products.
CROSMAN PELLGUNOIL MSDS
LUBRICATION ENGINEERS INC AD FOR MONOLEC GFS 8430 STATING "EXCEPTIONAL DETERGENCY"
SELF-CONTAINED PUMP : These models should be assembled using engine oil to lube all the seals and moving parts. Add a drop of oil directly into the pump chamber every couple hundred shots. You can do this more often if the piston isn't working smooth or produces inconsistent performance. If you accidentally over-oil you can fire the gun with the barrel pointed straight up, unloaded and safely away from you. In that position excess oil settles near the valve stem and blows out through the barrel. To prevent oil-lock, only use one pump for each shot until excess oil is cleared from the pump chamber and valve. A drop of oil should be applied to all pivot points of the pump lever and one at the back of the piston seal. This will lubricate the contact points of the pump assembly. The owners manual should indicate other model-specific lubrication points.
CO2 : Like the pump models above, these should be assembled using engine oil to lube all the seals and moving parts.
CARTRIDGE POWERED: For models with a piercing cap or rod that threads into the front of the gas tube, the threads should be oiled to keep them working smooth and prevent rust. A drop of oil should be placed on the tip of each cartridge before installation. For 22XX this prevents the piercing pin from getting stuck in the cartridge which keeps the cartridge stuck in the tube. It also lubricates the valve, ports and barrel to preserve performance and reduce corrosion. After installing a cartridge the gun needs to be fired once (unloaded) to pierce it. This is not a malfunction, it's how they are designed to operate. Other types of CO2 guns will pierce the cartridge automatically during installation.
BULK-FILL : A drop of oil should be placed in the fill nipple before each fill. This is not safe for dual-fuel PCP models. An explosion could occur during a rapid fill from an air tank. Refer to the PCP section below for more info.
SECTION 2 : PCP, HPA & BREAK BARREL
PCP & HPA : Without lubrication, PCP components can be difficult to assemble and o-rings are more easily damaged. Tanks are harder to install and remove without lubrication on the outer threads and o-rings. Many lubricants are not safe due to the risk of rapid compression autoignition. Use only lubricants that are recommended by the manufacturer or a trusted airgunsmith who works with PCP & HPA guns.
Crosman Silicone Chamber Oil (RMCOIL) is recommended by Crosman for their PCP guns. I found an even safer oil which is now available in my online store. It's currently the safest one in the industry for assembly and maintenance of PCP components. It's also safe for enternal threads and o-rings on HPA tanks. It's the same type as Crosman's oil but a higher flash-point version. Both are dimethyl, phenylmethyl siloxane, trimethyl-terminated. The version I offer has a higher phenyl content which gives it a much higher flash point and better thermal stability. It lubricates and prevents corrosion as well or better than Crosman's oil but is safer due to it's higher resistance to dieseling. I sell it in larger volume so it ends up being far less expensive than Crosman's version.
No lubricant should be used on internal threads of paintball tanks. They are commonly filled at extremely fast rates, an explosion could result. Scuba tanks generally have grease on the internal threads to prevent corrosion. They are filled at slower rates so there is no risk of explosion when the correct type of grease is used. Grease works better than oil for this purpose, it stays in the threads where needed instead of settling and migrating the way oil tends to.
It's not high pressure that causes lubricants to detonate, it's rapid compression generated during a rapid fill. The fill rate required for rapid compression autoignition to occur varies by the type of lubricant and size of the container. A PCP tube capacity of 4.5 cubic inches would require a rate of about 2000 PSI per second for engine oil to autoignite. The rate required for larger tubes is higher. The rate for smaller tubes stays about the same. Based on this it is safe to establish 2000 PSI per second as the minimum fill rate required to cause autoignition of engine oil. The rate required for common silicone oils is about the same, for some specialty versions it's much higher. Most silicone and engine oils are safe when there is no risk of accidental rapid fill. Only the safest type should be used otherwise.
BREAK BARREL : For most guns one drop of oil can be added as often as every couple hundred shots. Many will not require lubrication this often and some manufacturers recommend no oil at all. Some guns have a leather piston seal that needs to be oiled regularly. Some require petroleum-based oil and some require silicone-based. It is safest to fallow the manufacturers recommendation.
In February of 2017 I tested a new Crosman Steel Eagle right out of the box. It was .177 caliber and 6.9 grain pellets were used. The first shot was 1483 FPS and dieseled heavily. The second was 1428 FPS again with heavy dieseling. It took a total of about 10 shots for the dieseling to stop completely. After that it produced a ten shot string averaging 1031 FPS. The high was 1067 and the low was 997. Silicone oil was added to the chamber of this gun before it left the factory. The amount they added was the cause of the excessive dieseling at the beginning of the test. One drop would have burned off much quicker.
For the second phase of testing I added one drop of Mobil 1 10W30 directly into the compression chamber. The first shot was 1445 FPS with heavy dieseling. The second shot dropped to 1231, the third didn't sound like it dieseled at all but the FPS was still elevated at 1117. The fourth shot was 1085 and every other shot after that was between 1071 and 1087. The gun was more consistent, shot smoother and produced more power than it did originally.
The silicone oil I sell would not diesel in this gun. It produced about the same performance as Mobil 1 but seemed to last longer before needing to be oiled again. I have tested it repeatedly against Crosman's silicone oil with this and other guns. It produces more power, better consistency and lasts longer.\
If not done correctly, dieseling can cause damage to the gun and personal injury. Using a flammable substance can cause fire or explosion. Adding too much oil to the chamber or oiling too often can damage the piston seal and cause combustion residue to build up. Excess oil can work it's way around seals and combust outside the compression chamber where damage to the gun and personal injury could result.