Intentional dieseling test

[joneb]

I would not recommend that anyone would try this with a airgun they are fond of, and always wear eye protection while shooting.
While I have experienced unintentional dieseling in air rifles from over oiling I was curious if there could be a consistent effect from intentional dieseling.
The airgun I used for testing is a Hatsan 87 QE gas piston in .22 cal, the oil I used was Trader Joe's triple refined coconut oil. My tests were done at a range of 25 yds the chrono was five feet from the muzzle.
I shot five H&N FTT 14.66 gr on a target over a chrono,
h= 724 fps
L= 706
av= 714
es= 18
sd=7
The accuracy with this pellet in the 87 is so so about 1.25" @ 25 yds

I now tried the H&N FTT with the base of the pellet filled with coconut oil
h= 973
L= 960
av=966
es=13
sd= 4
The accuracy of this tighten up to .75" and the poi was about a 1/2" lower with the oil, the windage shifted a 1/4" to the left.

I did patch the bore after each group the oiled pellet did foul the bore but did not lead it.

I know that this seams like a bone head thing to do, but then I ask myself what would Elmer Kieth think?

 

[BilliamB.]

How does your rifle chrony now, after the coconut oil dieseling test? Any degradation in accuracy?

I believe some Mexican air rifles (Mendozas. perhaps?) are designed to use lighter fluid to deliver an extra wallop. I'd guess they'd use something other than Delrin as a piston material.

 

[edwardware]

I know that this seams like a bone head thing to do, but then I ask myself what would Elmer Kieth think?

If you start with that question, what could go wrong? Bravo!

While the solid coconut oil is easy to dispense, I would expect something more volatile to combust at lower initiation energy, perhaps more consistently. I also recall that coconut oil is destructive to some synthetic polymers (vinyl for sure. . .).

So, why coconut oil?

 

[joneb]

How does your rifle chrony now, after the coconut oil dieseling test? Any degradation in accuracy?

I believe some Mexican air rifles (Mendozas. perhaps?) are designed to use lighter fluid to deliver an extra wallop. I'd guess they'd use something other than Delrin as a piston material.

After the test I patched the bore and shot five of H&N FTT, I then shot three over the chrono on target. I saw no effect on accuracy,
h= 714
L= 705
es= 9
sd= 4
Sorry I should have shot five, I will do that when I get a chance.

 

[joneb]

If you start with that question, what could go wrong? Bravo!

While the solid coconut oil is easy to dispense, I would expect something more volatile to combust at lower initiation energy, perhaps more consistently. I also recall that coconut oil is destructive to some synthetic polymers (vinyl for sure. . .).

So, why coconut oil?

I thought it might be easier to get a consistent amount in the skirt of the pellet.
All the while I was thinking to my self, " what could possibly go wrong ".

 

[milemaker13]

Can you please explain dieseling in airguns?

 

[edwardware]

Adiabatic compression of a fuel-air mixture will, with sufficient energy, combust the fuel-air mixture. . . al la diesel engine.

The phenomena can also be seen in high speed video of ballistic gelatin behind high velocity projectiles that result in a rapidly closing temporary cavity. Some incorrectly attribute this to sonoluminescence, but it's actually adiabatic compression leading to diesel combustion.

 

[Stumper]

Once upon a time, before the europeans added greater restrictions, Weihrauch made an airgun that metered a dose of ether into the cylinder when cocked to intentionally diesel. Reported, accuracy was usable and it boosted standard weight .22 pellets approximately 200 fps faster than the same model sans ether but it did damage springs and piston washers(leather) over time requiring more service on the airgun.

 

[edwardware]

. . . Weihrauch made an airgun that metered a dose of ether into the cylinder. . .

Kind of shading the line into firearm. Just can't stand those engineers always developing new ideas that aren't yet addressed by regulation.

 

[joneb]

While the coconut oil is solid at around 80 deg. F it turns to a liquid around 90 deg. F.
Trying to think of something better that would stay put in the pellet skirt and not liquify and flow back into the piston chamber.
Would some type of grease work?
The velocity with the coconut adds about 250 FPS at 82 deg F that about doubles the muzzle energy.

 

[flightsimmer]

I get dieseling with 3in1 oil, you can hear and smell it.

 

[joneb]

Might try some beeswax?

 

[joneb]

Might try some beeswax?

The beeswax did not combust. I may melt some down and add flaxseed oil to lower the pressure required to get the mixture to combust the mixture.
The melting point of beeswax is around 144 deg F. I will attempt to make a paste and see if it ignites.

 

[Chevota]

I've done it but used WD40 for more umph. It's hard to get the ideal amt so it's just for fun. Motor oil is more consistant and grease even more so. Using motor oil I generally get 50-100% more power. Usually the thicker it is the less burn so less power but there's lots of variables. I rekon you could try all kinds of hotter fuels but I think WD40 is already too harsh if it's a coil spring gun. Gas spring guns prolly won't care about this abuse but you can also run into other probs. Like the piston rebounding all the way back and cocking again, which could be a bonus but it likely hits the trigger too hard. Another drawback is the main seal; can it take the heat? A Crosman with it's nylon or whatever seal is pretty tough, but a Weihrauch seal apparently has a much lower melting point and will likely fail. Others I can't say so i'd simply get a replacement seal and swap it when done playing. The breech seal usually cannot handle the pressure w/o dieseling, so more psi means more leakage. My suggestion is use a rubber O-ring and try to get lockup to work better, or put pressure on the barrel to seal it better, like a bench rest.
Yes you can put the oil in the pellets skirt which makes more much better metering and is not as harsh on the gun sicne the explosion is in the chamber, not the compression tube. It will also net more power per wt of fuel. There are lots of youtube vids of people doing this and all kinds of other (not parent approved) stuff to airguns. Stuff like making exploding pellets, which I may have pioneered, I mean I know nothing about.

 

[joneb]

I picked up two more potential propellants at the dollar store, Vic's vapor rub and vaseline. I will test these when I get a chance.

 

[Mauser lover]

mwahaha! I want to watch this thread! I'm not trying it with any of my airguns though!

Well... not right now anyway. I don't have a chrony. Yet.

 

[Bushpilot]

15 or 20 years ago I bought a couple inexpensive Chinese springers. The guns right out of the box were so heavily oiled inside that they dieseled continuously. Velocities were highly erratic and accuracy was mediocre but usable. The seals on both didn't last long...

 

[Hasaf]

Kind of shading the line into firearm. Just can't stand those engineers always developing new ideas that aren't yet addressed by regulation.

This got me to think about if this would work with the large bore airguns. I don't think it will because those work by expanding gas (cold), whereas the spring piston ones work by compressing gas (hot).

Possibly a large bore spring piston that is designed, as mentioned, to use a metered amount of liquid (or gas) propellant. . .

As mentioned, it would blur the line, but for people in areas with sever restrictions, it may work around the definition of a firearm written into the law.

 

[Mauser lover]

I'm not thinking we are trying to do anything illegal here. Just trying to hot rod stuff!

The Nitro (or whatever brand) gas piston would probably still heat up the compression side of the piston just fine to make this stuff burn. The other side of the piston will not be hot due to the aforementioned decompression, but I would think that as long as the compression is still happening to push the pellet, it would still diesel.

 

[JohnKSa]

Even if it did end up meeting the definition of a firearm, it wouldn't be illegal because making a firearm is legal in the U.S. as long as it is not an NFA firearm, and as long as it is not made with the intention of selling it.

Just be aware that in a worst case scenario, this can really wreck an airgun.

The key to this is getting some of the fuel to vaporize. Using heavy/thick lubricants is going to be problematic because it's going to be hard to ignite them. The temperatures do get very high, but only for a very short instant of time. Consistent ignition will require a vapor/air mix.

 

[desidog]

So... i understand if the dieseling occurs behind the projectile it increases the velocity ala gunpowder... but if residual oil is left in the barrel after cleaning, does the dieseling event occur in front of the bullet in the barrel and slow it down?

 

[flightsimmer]

So... i understand if the dieseling occurs behind the projectile it increases the velocity ala gunpowder... but if residual oil is left in the barrel after cleaning, does the dieseling event occur in front of the bullet in the barrel and slow it down?

No.
It is not sufficiently compressed.