Gas systems, oiled or dry?

[briansmithwins]

So, I'm curious about the common wisdom about leaving gas systems dry vs oiled.

First we have the gas piston from a Steyr AUG as removed when the gas system wasn't lubricated between shooting sessions. Total of about 100 rounds fired over 3 shooting sessions.



This is the same gas piston after rubbing with a dry soft cloth. No solvent of any type was used to clean it.



Next is the gas piston after adding 1 drop of oil* to the gas piston after each shooting session. About 120 rounds fired in 3 shooting sessions. The piston wasn't removed to apply oil, I just did one drop on the face of the piston. The oil has crept over the entire surface of the gas piston and the whole thing is oily.



This is the same gas piston after rubbing with a dry soft cloth. No solvent of any type was used to clean it.



There wasn't appreciably more carbon on the piston after applying oil and then shooting it. What carbon there was was much easier to remove after it had the oil on it.

BSW

*Aeroshell Fluid 18

 

[bainter1212]

Well I think you answered your own question.

I coat with oil and then wipe clean so there is no excess, just the lightest of film to protect the metal surface.

 

[HammsBeer]

I apply a light film of oil to gas pistons after cleaning. If I shoot the rifle but don't plan to clean it right away, I will pull the gas piston out and apply another film of oil to it, mainly for corrosion protection.

I learned the hard way when I shot my mini 14 and just put it away. A couple months later the gas op rod was stuck to the gas piston and it took considerable force to bust it loose. No permanent damage but I always reoil it right after shooting now.

 

[MistWolf]

Back in the day when Garands, then M14s ruled the world, the general advice was to not oil the piston because it was thought that it could combust from the hot gas and would damage something

 

[hq]

I coat with oil and then wipe clean so there is no excess, just the lightest of film to protect the metal surface.

I concur. Additionally, when I have spare time in my hands, I sometimes polish gas pistons and tubes. The smoother the surface, the less carbon residue will stick to it and the easier it'll be to keep clean.

 

[itsa pain]

I apply a light film of oil to gas pistons after cleaning. If I shoot the rifle but don't plan to clean it right away, I will pull the gas piston out and apply another film of oil to it, mainly for corrosion protection.

I learned the hard way when I shot my mini 14 and just put it away. A couple months later the gas op rod was stuck to the gas piston and it took considerable force to bust it loose. No permanent damage but I always reoil it right after shooting now.

The AK gas piston will freeze up also

 

[benEzra]

When my primary rifle was an AK, I always lightly oiled the gas piston and piston tube for corrosion protection. I did find that this also made it easier to keep clean.

I do not put oil in the gas tube of my DI AR, but I put a drop in the bolt carrier key and generously oil the bolt and bolt carrier (which includes the piston and gas rings).

 

[Cowboybebop]

I've wondered this as well

This question has always bothered me, here's why:

The M1/M1a/M14 crowd says to run gas systems dry, or else they will attract carbon and seize up. The Springfield M1a manual repeats multiple times that the piston and cylinder are to be assembled completely dry, and that the system was designed to be run that way.

The HK416/MR556 manual specifically tells you to lube the piston and gas cylinder with a medium coat of CLP. This is the exact opposite of the M1 advice.

The Auto Ordnance M1 Carbine manual instructs to wipe all surfaces with an oiled cloth. No special instructions for the gas system - implying that it is to be oiled as well.

The FN FNAR manual tells you to rub the piston/gas cylinder down with a lightly oiled cloth before reassembly. Additional lubrication "could interfere with the function of your rifle." No mention of damage.

The FN FS2000 manual instructs you to oil the piston shaft, but not the piston face. No warning about what will happen if the piston face is oiled, however.

The FN SCAR 16S/17S specifically advises against lubricating the piston and/or gas cylinder and even warns that it will DAMAGE the rifle. This is the only design I am aware of where the manual actually mentions potential damage.

The Ruger Mini-14 and SR-556 manuals advise that ALL PARTS should be lightly oiled after assembly, including running a lightly oiled patch through the bore. No special mention of gas system - once again implying that it should be oiled as well.

Bushmaster AR-15 manuals instruct the user to drop CLP into the gas key, which seems to go against the idea that oil in contact with hot gases creates carbon fouling. In addition, I have not found an AR-15 manual that warns against oil inside the gas tube, which implies that it is not a problem.

The M240B light machine gun manual (FM 3-22.68 chapter 3) says that the gas system should remain completely dry after assembly. Comments from guys in the field seem to indicate that this instruction is actually important, as the gun could seize up if oil is present. I can't verify this observation personally.

As you can see from above there is a lot of conflicting data on whether oiling the gas system is recommended. As to the reasoning of why oiling the piston/cylinder could cause damage I have heard the following explanations:

1. The lubricant could self-combust due to dieseling and cause excess pressures in the gas cylinder.

2. The lubricant can cause excess hydraulic pressure and rupture the cylinder.

3. The oil burns off due to the heat of the gases and fouls faster than normal.


I don't tend to buy into answers 1 and 2. But maybe someone more knowledgeable can chime in here. It seems to me that dieseling and hydraulic pressure would not be an issue with the gas vent being open to the atmosphere, but I am not an engineer.

Number 3 makes sense to me, because I have seen some smoke during the first couple of rounds from my Mini-14 when the piston was oiled. Something was definitely burning off. But I have never had a problem wiping off the carbon during field strip.

Could it be possible that the warning in the SCAR manual about possible damage is simply the designers worried that the piston will foul so badly that it will stick?

The OP's round count on the oiled piston is not low - I would think that after >100 rounds any problems would begin to surface.

 

[Ifishsum]

I believe in using a light coat of oil on the piston and rod, and the M1 manual I received with my CMP rifle suggests applying a very thin coating of light grease on the last 3-4 inches of the op rod to make cleaning easier (and it does).

My first gas gun was an SKS, and I remember reading somewhere that the piston should be kept DRY and never oiled. I can tell you that after a few hundred rounds it was a real PITA to clean, thereafter I started oiling it very sparingly and the fouling practically wiped right off - even the hard fouling that I couldn't remove before was gone. I imagine too much oil could case problems with some designs but a light application is beneficial as far as I am concerned.

 

[HammsBeer]

The thin film of oil on the gas piston system is for corrosion protection in storage. I don't bother cleaning off the oil before shooting. The first few shots the oil burns off and the system will be dry after that. After shooting I reapply a film of oil to the gas piston before putting it away.

I don't buy into "dieseling" or "hydraulic shock". It just burns off with heat.

 

[Dr. Sandman]

+1 for just a drop.

 

[W.E.G.]

You can't "oil" a gas system on a rifle.

All you can do is apply preservative to lessen the chances of oxidation during storage or non-use.

With the exception of the AR15 gas tube, I hose my rifles' gas systems with Break-Free, and then I remove the excess by compressed air or wiping. This has provided me with good results in rust avoidance.

 

[Slamfire]

So, I'm curious about the common wisdom about leaving gas systems dry vs oiled.

Back in the day when the M1a ruled the firing line, the advice I most commonly heard was to keep your gas piston dry. I wondered about that and why. Perhaps my greatest problem is I over oil my rifle mechanisms. I shot a AR15 match rifle this weekend and I had so much oil on my shooting glasses that I had to use glass cleaner to remove it from the lens. My shooting data book has little dark spots from the oil spray. This behavior is typical with me: I am incorrigible. :banghead:

So, being of an unsound mind with unsound practices, I oil the gas piston in my M1a's. Just a light coat, excess oil drips off. First shot standing there is always a plume coming out of the gas cylinder. By the end of the day I am certain there is no oil left and I am not sure the oil improved anything, such as reduced wear. But it could have, and that is the important thing.

Now, in my studies of this, I think this dry piston versus wet piston was an internal dispute within Springfield Armory and the dry piston guys won. Design bureaus come up with sacred cows, sometimes these sacred cows are nothing more than BS created by massive egos who have to "win". From what I read, SA stated that under pressure the gas pistol "floated" inside the gas cylinder. Of course this is wonderful, brilliant beyond reckoning, as that would make the gas pistol and gas cylinder last forever. Reading into this, it becomes obvious that the piston must run dry or all that cleverness that went into designing this magical device would be defeated by evil nasty oil.

There could be a case for oil congealing and gumming up the gas system, but, this has not happened to me, and by the time the oil in the gas system gummed up, so would have all the other oils and greases in the rifle.

You have to maintain these things you know.

 

[HammsBeer]

I'm not familiar with a floating gas piston in the M1A, but I could see oil sludge causing problems in a multi-part self-regulating gas sytem. Both my Mini 14 and Adams Arms piston AR use a basic non regulated gas port and fixed piston in the front gas block, and the piston op rod slides over it.

 

[wally]

This question has always bothered me, here's why:

The M1/M1a/M14 crowd says to run gas systems dry, or else they will attract carbon and seize up. The Springfield M1a manual repeats multiple times that the piston and cylinder are to be assembled completely dry, and that the system was designed to be run that way.

The HK416/MR556 manual specifically tells you to lube the piston and gas cylinder with a medium coat of CLP. This is the exact opposite of the M1 advice.

The Auto Ordnance M1 Carbine manual instructs to wipe all surfaces with an oiled cloth. No special instructions for the gas system - implying that it is to be oiled as well.

The FN FNAR manual tells you to rub the piston/gas cylinder down with a lightly oiled cloth before reassembly. Additional lubrication "could interfere with the function of your rifle." No mention of damage.

The FN FS2000 manual instructs you to oil the piston shaft, but not the piston face. No warning about what will happen if the piston face is oiled, however.

The FN SCAR 16S/17S specifically advises against lubricating the piston and/or gas cylinder and even warns that it will DAMAGE the rifle. This is the only design I am aware of where the manual actually mentions potential damage.

The Ruger Mini-14 and SR-556 manuals advise that ALL PARTS should be lightly oiled after assembly, including running a lightly oiled patch through the bore. No special mention of gas system - once again implying that it should be oiled as well.

Bushmaster AR-15 manuals instruct the user to drop CLP into the gas key, which seems to go against the idea that oil in contact with hot gases creates carbon fouling. In addition, I have not found an AR-15 manual that warns against oil inside the gas tube, which implies that it is not a problem.

The M240B light machine gun manual (FM 3-22.68 chapter 3) says that the gas system should remain completely dry after assembly. Comments from guys in the field seem to indicate that this instruction is actually important, as the gun could seize up if oil is present. I can't verify this observation personally.

When in doubt, RTFM and follow its instructions!

Seems simple. Different recommendations for different designs is not unreasonable.