Some talk about airgun lubrication: Part 1
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- Why do we lubricate?
- The Meteor’s needs for lubrication
- Leather piston seals
- Watch the performance
- Synthetic piston seals
- Other lubrication requirements
Yesterday a reader asked why I bothered with Tune in a Tube. Why didn’t I just clean the Meteor Mark I when I had it apart, lubricate with moly grease and be done with it? That tells me there are a number of readers who don’t really understand what is involved with airgun lubrication. So today I thought I would discuss it a little.
Why do we lubricate?
This is a good place to start. In fact, from the reader’s comments, it seems to be at the core of misunderstanding. Don’t we just lubricate to reduce friction?
Friction is a principal reason for lubrication. But there is more to it than that. Sometimes we want to reduce friction by a certain amount, while retaining some part of it that’s needed for proper operation. Otherwise, moly (molybdenum disulphide) would be the answer to everything. Some airgunners think it is. The reader who wrote the comment that got me started on today’s topic said that very thing — that I should just clean the Meteor’s parts and lube everything with moly and be done with it.
That would be a disaster! Let’s look at that airgun and see why.
The Meteor’s needs for lubrication
The Meteor was buzzing when it fired. Buzzing is caused by excessive tolerances that allow the powerplant parts to vibrate when the gun fires. Moly will have no affect on that. The parts may move faster than they did before when lubed by moly, but they will still bang together and vibrate in an annoying way.
What is needed is one of two things. Either the parts must be tightened in some way so there is less sloppiness or they must be surrounded by a material that causes the vibration to stop quickly. Tune in a Tube does the latter. While it does provide lubrication, the ability to stop vibration is its principal feature. Add to that the fact that it can be applied to a gun without disassembly and you have a wonderful product for a spring piston airgun. And a mediocre one for a CO2 or pneumatic gun, whose needs for lubrication are different.
I will address those other powerplants later in this series. Let’s stay with the Meteor for now. The Meteor is made as cheaply as it can be. Its piston is sheet metal that’s formed into a cylinder and welded, top and bottom. That kind of construction does not lend itself to the attachment of synthetic bearings called buttons, which are the number one way to eliminate slop for a piston . You saw me use buttons on the piston of the Diana 45 I tuned in the special 10-part series I did last year. Part 6 of that series shows most of the tricks I would normally use to tune a spring gun, but the Meteor’s thin metal construction doesn’t allow most of them. Because of that, Tune in a Tube is an ideal product for the Meteor. The intended use is a large part of selecting the correct lube.
For the Meteor piston, piston seal and mainspring I need a lube that will dampen vibration, reduce friction and also seal the compression chamber. Tune in a Tube with do the first two, and oil will seal the compression chamber. But — what kind of oil? The Meteor has a leather piston seal, so let’s discuss that first.
Leather piston seals
Leather piston seals need to be flexible to seal the compression chamber. That takes oil. Is the oil a lubricant? Yes, but in this case it’s being used for three good reasons. First, because it keeps the leather seal pliable, allowing the leather to flex and to therefore seal the air in front of it. Second, being oil, it lubricates the seal, reducing friction so the seal and the piston it’s mounted on will move as fast as possible. And third, being oil, it evaporates slowly, which means the seal will stay pliable longer. But longer than what? Well, longer than water, for example.
Water will lubricate the leather and make it pliable. A water-soaked piston seal will seal the compression chamber about as well as one soaked in oil. But water evaporates rapidly and will dry out. When it does, the leather will shrink and harden. If left that way, it will break up in small particles every time it is moved, as in firing. And, if left for long enough it will eventually dry completely, allowing the leather to deteriorate by a process we call dry rot. Oil may dry to a point, but even when appearing dry some will remain for years, preserving the leather if it isn’t worked too hard. I have seen the leather seals in airguns that were over one-hundred years old, and they were still in working condition because they had been oiled.
The velocity of the airgun also plays a factor in the choices for lubricants. The Cardews showed in their experiments that were documented in the book, <i>The Airgun from Trigger to Target</i>, that when a spring piston airgun approaches 600 f.p.s. muzzle velocity it starts burning some of the lubricant in the compression chamber. That is called dieseling. Like any other internal combustion engine, this burning of oils generates energy of its own. In an experiment the Cardews shot a 14.4-grain .22-caliber pellet in an HW 35 at 636 f.p.s. when the gun was properly lubricated. When the same gun was fired in a pure nitrogen atmosphere where combustion was not supported, the same pellet only shot 426 f.p.s. This proved that combustion was generating part of the energy in that airgun.
My BSA Meteor Mark I shoots light lead pellets at greater than 600 f.p.s. So it is safe to assume that it, too, is dieseling with every shot. If water was used on the leather seal, the gun couldn’t diesel and the resulting velocity would be much slower. But consider this. If I used a type of oil that combusts readily, such as one made from petroleum, the gun might go from dieseling to detonating, which means exploding with every shot.
Therefore, for guns that shoot in the high 400s to the mid-500s, like Diana 25s and 27s, I recommend a piston seal oil that’s petroleum-based, like Crosman Pellgunoil. For guns that approach 600 f.p.s. and more I recommend high-flashpoint silicone chamber oil. Now you know the answer to what oil to use in a spring gun that you suspect has a leather piston seal. It’s based on the gun’s potential velocity, and if you don’t know what that is, watch the performance of the gun after you oil the piston.
My final comment about water on leather seals — don’t do it! That was mentioned for the purpose of discussion, only. Water inside a spring gun would rapidly oxidize and cause the gun to rust.
Watch the performance
If the gun you have oiled smokes after each shot without any noise, you are using the right type of oil on the piston. It may detonate a few times at first, but two or three explosions is all you should hear. If it keeps on exploding, you used the wrong type of oil. Since the seal is leather, just wait a few months, then oil it with silicone chamber oil from then on.
Synthetic piston seals
The oil for synthetic piston seals does something different than the oil for a leather seal. A modern synthetic seal is self-lubricating, which really means that the seal material has a very low coefficient of friction. It doesn’t need oil to work its best — at least not from the standpoint of friction.
A synthetic seal uses oil as an additional air barrier between the edge of the seal and the compression chamber. Like the oil in your car’s engine, the oil in your airgun compression chamber just makes the piston seal better. Don’t use too much oil, though, because the act of firing will vaporize some of the oil and cause it to detonate inside the compression chamber.
Synthetic seals come in all modern airguns, but since most of them shoot faster than 600 f.p.s., I advise everyone to use silicone chamber oil for their seals. It saves me having to explain all that is in this report, every time I talk to a new airgunner.
Today we have discussed lubricants used for two purposes. The first is to reduce vibration between moving parts in a spring-piston powerplant. And the second is to lubricate the piston seal.
When it comes to the piston seal we discussed the three purposes for oiling leather piston seals, and what types of oils work best. We learned that it depends on the power the gun produces. We also discussed what lubrication does for synthetic seals, and how that differs from the needs of leather piston seals.
I held nothing back today. If this report put you to sleep, my advice is to have someone else tune your spring guns. And, I’m just getting started. There are other lubrication requirements that deserve a thorough presentation as well.
Other lubrication requirements
Sealing pneumatic and gas reservoirs and valves
Reducing friction on metal parts
…heavy wearing parts like linkages
…piston bodies and spring guides
As you can see, there is a lot to lubricating airguns, and I plan to tell it all.