Lube dieseling

[Goatwhiskers]

Late nite idle thinking. Read about this in another thread. Referring back to a thread I had posted earlier about some accuracy problems when I shot a plain based version of a GC boolit that had given me great acuracy. Not only had a pattern like buckshot, just remembered every shot gave a cloud of smoke almost like shooting black powder. Ya think I might have had this condition? Couldn't have helped accuracy much. Oh yeah, I was using LLA for lube, tumble applied. Goat

[uscra112]

Lube dieseling is a big problem in air guns, but the amount of energy it could add to a smokeless powder load would be miniscule as a percentage.

[MBTcustom]

Now I've heard everything! It makes sense (for air rifles that is).
I love this site!

[Wolfer]

When I get the black powder look my first thought is my pressure isn't high enough for my powder to burn right.

[DrB]

To have dieseling you have to have 1) fuel 2) air (oxydizer) 3) ignition (technically, to be dieseling you need adiabatic compression of a fuel/air mixture to the autoignition point.... in the case of a combustion chamber already containing burning propellant, it's not dieseling).

I am certain some lube will react with the hot gases/air in your charge. In order for it to cause accuracy problems I would expect it to have to either result in damage to your bullet or inconsistent round-to-round velocity.

I am sceptical of lube combustion significantly changing chamber pressure such that it was a significant problem, and if it was, it still probably shouldn't be called "dieseling" because it isn't.

Dieseling is more significant in a spring-piston gun because the volume of air is more significant, and if excess lube/oil has been left in the spring piston chamber you can actually get a pretty significant diesel detonation, which isn't what the system is designed for (and will be HIGHLY dissimilar in resulting pressure/time history from a non-dieseling shot and therefore inaccurate). Further, unless you have a very consistent means of controlling the fuel/air amounts, mixing, and ignition, then even if every shot did diesel it would probably do so significantly differently, thus destroying shot-to-shot consistency and accuracy. Dieseling is bad mechanically and in terms of accuracy with any airgun not designed to do so.

In a firearm I too suspect the percentage of contribution to MV of lube/air combustion would be small with anything but the very lightest squib load... and I don't know that it would be significant then. It wouldn't be hard to calculate the adiabatic pressure resulting from a slightly fuel rich wax/air mixture given the volume of air available in a loaded case. I believe a tool like propep would also allow you to do the same for various fractions of nitrocellulose.


Best regards,
DrB

[HangFireW8]

That reminds me of my happily mispent childhood, shooting a cheap Daisy lever-cock BB gun (not an air rifle as there was no rifling). One day my zealous lubrication of said shootin' iron resulted in a diesel ignition and a really, really flat trajectory. Well, it was off to the races, for a few days I carried the oil can with me shooting and tried to get it to happen as often as possible. Finally I gave up when I realized the result was even greater inaccuracy than usual- and for a smooth-bore with a 6 inch actual barrel, that's pretty bad.

Anyway, Alox lubes are well associated with smoke, LLA or 50/50 or otherwise. If it was really bad you may have had some damp powder.

HF

[badbob454]

great stuff love to read all this stuff, i had a old sears pump 22 if i oiled it real good the first few were pretty hot , also my 22 rimfire seems to do the same if oil is left in the barrel fresh after cleaning it , yeah i know im supposed to wipe it clean

[geargnasher]

Sounds like typical smoky LLA/gunpowder to me. Often, much of the smoke is from the powder, the lube just seems to make it worse. Note any ash left in the barrel. I don't know what the flash point of dried LLA is, but it might be possible for it to truly diesel in the grooves, since you will have air, fuel, and many tons per square inch of pressure in the grooves as the boolit travels down the bore, unless you have perfect gas sealing of the boolit base, which is just about impossible.

Gear

[303Guy]

I theorise that an oily chamber causes high bolt face loads due to dieseling. Ok, it's not actually dieseling as the ignition source would be the powder. However, the oil mist sprayed into the fire could add a significant amount of energy to the system. The main fuel would be hydrogen which could result in a faster burn and higher energy release with more unburned carbon. I'd think there would be excess oxygen in powder. Maybe not.

[DrB]

An oily chamber can be demonstrated to result in more bolt face loads due to the brass not gripping the chamber... reduction in load transfer to the chamber walls through friction increases bolt face loads, and if the seal at the neck is lost that can increase the pressurized area as well. Didn't ackley experimentally demonstrate this one pretty well?

Oil by itself I wouldn't expect to do much but drop chamber pressure. The purpose of a smokeless propellant is to produce pressure via hot gas...if the propellant were very fuel lean such that more fuel would help, it would be a trivial thing to improve the formula by adding a little fuel rich material. While the addition of oil might make a small increase in some particular circumstance, it seems pretty unlikely to me in the general case.

I had dieseling with my 22 cal rws 48. Yeah, it was notably louder, and faster! Never did get that one to shoot well (dieseling or not)... poi seemed super dependent on how I held it and accuracy suffered (spring piston recoil threw shots before the pellet left the muzzle). Seemed a little odd to me as I had a cheapo spring piston airgun as a boy I shot so much I could hit a running squirrel in an oak top without thinking about it.

Best regards,
DrB

[303Guy]

As far as I know Ackley did tests with a lever action 30-30. He didn't do oily chamber tests as far as I know. I've also wondered whether the oily chamber could be floating the case and actually driving it back. I've fired a cartridge without the bolt in place and the head flew off leaving the case body behind (I won't go into how I did it). There wasn't a lot of powder in the case either. That was a lubed case like I always use.

[runfiverun]

i am still thinking the dieseling is occuring on the front of the boolit and not the back end.
i know that the bbl is open to the air but oxygen is required for stuff like that.
the boolit rushing down the bbl building up lube on the front of it could compress air in an open area.
30-1 dunno, but dieseling could refer to the way a gas engine knocks too.

[waksupi]

I'm thinking your condition was caused by changes in temperature and humidity. LLA will only work well in limited applications.

[44man]

i am still thinking the dieseling is occuring on the front of the boolit and not the back end.
i know that the bbl is open to the air but oxygen is required for stuff like that.
the boolit rushing down the bbl building up lube on the front of it could compress air in an open area.
30-1 dunno, but dieseling could refer to the way a gas engine knocks too.

That is what I as thinking. There is tremendous compression ahead of the boolit. It would not be enough to add or subtract from anything but it could burn any lube left in the bore. Might be proven with slow motion video to see if any smoke exits before a boolit.
Either way, I figure smoke is burning lube whether in front or behind a boolit.
It was just something I was thinking about, no proof whatever but could lube diesel behind a boolit? Conditions might be good since powder produces it's own oxygen.
Remember a diesel engine works with low compression compared to the many, many thousands of pounds in a gun.
I know, I always throw in a monkey wrench for thought.
Now this is not like a lubed chamber or brass that prevents the case from holding against the chamber and increasing thrust or oil in the bore that reduces friction---BUT, can the oil diesel?
What concerns me is more fouling and ash left in the bore then powder alone leaves behind. I know LLA gives me leading and poor accuracy in my revolvers. The addition of beeswax seems to increase the flash point.
The question I have is does compression lower the flash point of LLA?
I have a test chart here somewhere where all lubes were tested in BPCR's. As the flash point of lube components increased, so did accuracy and a reduction in fouling. The addition of soaps helped.
Those expensive lubes with a lot of paraffin failed as did SPG, leaving half the bores so fouled a patch could not be forced through unless wet.
Some will blame powder efficiency, not so. Too slow a powder and a short barrel can leave unburned powder behind but it is not the same fouling. Just loose particles. Any powder fully consumed has a finite amount of carbon, it can not increase.
Carbon has many forms, some will lube, other forms are abrasive all the way to diamonds that cut anything. What kind of ash does LLA leave behind?
Some use bearing grease in lubes but some with soaps will not melt in. You can turn it to smoke before it melts and will ruin any wax.
Maxi balls are sold with lube on them. The stuff dries out. The package says it will still lube if dry and that is so much bull it is unreal.

[Certaindeaf]

The ether injected Weihrauch EL-54 spring piston is pretty neat.

[HangFireW8]

I've fired a cartridge without the bolt in place and the head flew off leaving the case body behind (I won't go into how I did it). There wasn't a lot of powder in the case either. That was a lubed case like I always use.

Here's something to think about. If there was more powder in the case, and it wasn't lubed, there would be a chance the case would have stayed together.

HF

[Glen]

One key difference to keep in mind in this discussion -- in an air gun the compression is taking place under oxidizing conditions (i.e. there is surplus oxygen around to support dieseling). In a firearm, once the powder deflagration is complete the conditions are, in fact, net reducing, and there is no free oxygen to support dieseling.

[W.R.Buchanan]

Just so it is completely understood: Dieseling in airguns ONLY applys to guns that compress the air when fired. IE: spring piston or gas piston guns.

Precharged Pneumatic and CO2 powered guns only release air which is disapating energy, not compressing the air to raise the heat.

If you release compressed air it is cold not hot. Verify this next time you release the air from a tire. There is no heat to induce dieseling on a PCP gun.

Randy

[DrB]

Now, ignition from air compressed in the bore sounds a bit more plausible to me, though I don't understand how it would be a problem. If that was what the op was suggesting I missed it.

I don't know that high speed photography would tell you anything conclusive, as you see video of jacketed/artillery with a puff of smoke preceding the bullet and uncorking. I always figured it was low volume leakage.

There is an old agardograph with analytical solutions of I believe maybe this particular problem (unconstrained gas compression in front of a moving piston) and similar ones like light gas guns.

If there is data that relates actual autoignition temp and performance as a lube that is interesting, though I would wonder if it was just a proxy for another metric like hydrocarbon chain length. Autoignition temperature goes down with increasing hydrocarbon chain length. Viscosity goes up.... So lower chain lengths will flow better AND be more resistant to autoignition. Correlation didn't mean causation, lower viscosity may be the needed thing, and autoignition is just a red herring.

[Larry Gibson]

I concur with DrB 100%;

"I am sceptical of lube combustion significantly changing chamber pressure such that it was a significant problem, and if it was, it still probably shouldn't be called "dieseling" because it isn't.

The bullet lube on the base of a bullet would be consumed during and with the combustion of the powder. It would not be a seperate "combustion" in and of itself caused by the powder combustion presure. Unless one wants to consider going off on a tangent about "ringing" of chambers when a wad is used instead of a filler. There a plausible (?) explanation could be deiseling. There is a bit of lube, oil or other combustable is on the base of the bullet. the wad is driven forward compressing the air in front of it against the base of the bullet, the heat from the compression detonates the lube and voila....a ring from the high psi in that area of compression and "deiseling"........Now, before everyone jumps my case that is not my theory as I heard some time back......I'm just the messenger here......

Larry Gibson