Two UNPROVEN thories about flint ignition

[Larry Pletcher]

Steve Chapman and I compared notes last night and got some ideas together.  We will probably use Steve's rifle because it already has mounts for high quality target sights.  We have a couple of 1/16" liners to choose from.  He also has a good ball patch combination in use which saves some experimentation.

We will incorporate a number of steps to rule out variables:
weighed charges and balls
uniform seating pressures
wiping between shots
etc

Steve will do the shooting as he is really tuned in to this rifle. After chrongraphing the  the accuracy load we'll drillout the vent and chronograph again and measure the group.  The results of this step will tell us what our next step will be.  

We both have time issues that will delay this experiment for a time.  THis isn't a cop-out; we both are really curious what we'll learn here.  Our past experiments have been easier to get together on than this next one will be.

Regards,
Pletch

[Daryl]

Sounds great, Pletch - I'm really looking forward to seeing your results - as usual.

[Mad Monk]

Steve Chapman and I compared notes last night and got some ideas together.  We will probably use Steve's rifle because it already has mounts for high quality target sights.  We have a couple of 1/16" liners to choose from.  He also has a good ball patch combination in use which saves some experimentation.

We will incorporate a number of steps to rule out variables:
weighed charges and balls
uniform seating pressures
wiping between shots
etc

Steve will do the shooting as he is really tuned in to this rifle. After chrongraphing the  the accuracy load we'll drillout the vent and chronograph again and measure the group.  The results of this step will tell us what our next step will be.  

We both have time issues that will delay this experiment for a time.  THis isn't a cop-out; we both are really curious what we'll learn here.  Our past experiments have been easier to get together on than this next one will be.

Regards,
Pletch

OK Pletch,

First play with piles of powder on sheets of white paper.  Use a heated wire for ignition.  First light a pile of powder in the center of the pile.  Burning grains of powder will be ejected from the pile in a 360 degree circle.  Then light another pile from one edge.  You see the buring grains being blown away from the point of ignition in roughly a 280 degree to 300 degree direction.

An old QC test in powder plants was to place two measured samples of powder on a flat surface a certain distance apart.  Then ignite one pile and see if the other pile ignites.  Keep increasing the distance until the second pile does not auto-ignite.

Part of what this old test was looking at was ease of ignition of a specific sample of powder.  This will be affected by the amount, or thickness, of glaze on the powder grains.  For the same brand of powder.  2Fg will be harder to ignite compared to 3Fg.  1Fg will be harder to ignite compared to the 2F and 3F samples.  The larger the grain size the thicker the "glaze".

An Aberdeen proving Ground BRL paper described the ignition of black powder grains as seen using high-speed photography.
Using a spark as with a flinter or a heated wire.
Where the heat source touches the surface of a grain there will be a small "puff" of "smoke" seen only with IR photography.  This is a bit of water being vaporozed by the heat.  Most of any water in the powder will be found trapped in the skin, or glaze" on the surface of the grains.  A portion of the skin will be melted by the heat.  The melted portion will then glow a dull orange or red color.  Then you will see actual combustion of the powder grain begin.

The powder is 75%, or more, potassium nitrate.  In order to gain ignition of the powder you must first heat a portion of that potassium nitrate, on the surface of the grains, to its melting point and then continue heating until you reach the decomposition temperature of the potassium nitrate where it will then evolve oxygen to promote/sustain additional powder combustion.

The Aberdeen papers also point out that black powder combustion is not influenced by pressure when it burns.  Increasing the pressure in the container holding the powder does not increase the rate of ignition or combustion of the powder.
But with the relationship between heating and powder combustion the temperature of the powder charge at the time of ignition will effect how fast the charge ignites and burns.  Simply due to the fact that you have to pump fewer calories of heat into the powder to get it up to the combustion temperature as promoted by the decomposition of the potassium nitrate.

Bill K.

[Larry Pletcher]

Hi Bill,
Great information.  I have done the paper test when you recommended it a while back.  The burn pattern is just as you describe.  Give this a try, guys; it's pretty cool.   This is the reason I tend to think of the barrel charge and the pan charge as one charge instead of two.  They are so close together that they act like Bill's paper experiment.

As always I learn something new when ever I read your notes.  The following quote says a bunch:

The Aberdeen papers also point out that black powder combustion is not influenced by pressure when it burns.  Increasing the pressure in the container holding the powder does not increase the rate of ignition or combustion of the powder.

This has been a revelation, but begs more questions.  Does this mean that seating pressure has less effect than we think? 

Or this quote:

But with the relationship between heating and powder combustion the temperature of the powder charge at the time of ignition will effect how fast the charge ignites and burns.  Simply due to the fact that you have to pump fewer calories of heat into the powder to get it up to the combustion temperature...

Perhaps this means that the ignition speed increases as the barrel temp increases.  We may have thought as velocities increased in a series of shots that is was because of slight increases in fouling when the real reason was the increase in barrel temp.  Am I reading this correctly?

Regards,
Pletch

[Dr. Tim-Boone]

I thought about the barrel temp variation too, when I read that........ a goal of consistency of accuracy would seem to argue for a slow rate of fire (max cooling time) and perhaps regular wiping with a wet patch...... to cool as much as to control amount of fouling???    I wonder how big the variations in powder temp need to be to significantly influence ignition speed and perhaps pressure???

I bet the powder compression does have less effect than commonly believed. verrrryy interesting.

[Mad Monk]

Larry,

Think back to our early conversations on differences in powders actions in the pan of a flintlock.  My experiments in the dark basement.  With GOEX in the lock I could see the flash of the powder when I cycled the lock but could not see any light with the Du Pont Eagle Brand Sporting Powder in the lock and that with the Eagle powder I could feel a wave of heat hit my face.
I had read one paper that talked about black powder combustion creating a wave of radiant heat.  This wave of radiant heat would travel away from the powder at a speed faster than the flames and flying incandescent debris.
Not mentioned but I suspect that the radiant heave wave is what sets off a pile of powder next to one being ignited.

Seating pressure.
Keep in mind we are dealing with a granular propellant that does not take the form of perfect spheres.  There will be variations in packing density in a charge of powder.
When I would run loading density on a powder sample I would pour the sample into a 50 ml graduated cylinder.  Run a spatula over the top to level it and remove the excess above the rim.  Then weigh that.  Do 10 of them and calculate the loading density as g/cc.  As is done in the industry.  Then another set of 10 where I would gently tap the side of the cylinder while slowly pouring powder into it.  This taping, or bumping, would settle the grains of powder to give what is thought to be maximum nesting.  Then weigh those and calculate loading density as g/cc.
In this you will see some powders settle as much as 10% of the original volume.  Some as little as 1 or 2 percent settling.

Remember that the charge is being burned under confinement.  So if you can get the powder charge into a smaller amount of space in the bore you have increased its "degree of confinement" and get a bit higher velocity.
But in ther gun you should have the exact same "degree of confinement" with each charge.
In dealing with a granulated propellant where the grains are very irregular in shape you will have almost 10 different weights if you measure by volume and 10 different volumes if you measure by weight.  The theory was that you have to have the exact same amount of powder occupying the exact same amount of space for best accuracy as determined by uniform shot to shot muzzle velocities.

This is why a lot of bp cartridge shooters weigh charges.  Use a drop tube of a specific length to insure maximum packing and then compress the charge to fit into an exact amount of space in the case.

The big kick in the late 19th century was to produce a black powder with perfectly spherical grains to do away with the variations created by odd-shaped irregular grains.  Trouble is that there is now way to do this spherical grain thing with a press densified powder.  You can do it with the powder in process but then you have no way to press densify it.  Without press densification the powder will be a bit weak and erratic in the gun.

You may remember the Ka-Doty (spelling???).  The whole idea to that was to pack the charge into the same space each time you loaded the gun.  This concept sometimes used springs or falling weights to pack the powder grains as tightly as possible into the smallest space and do it exactly the same each time.


Barrel temperature??

When I was doing the fouling work I found that barrel temperature had little to do with what percentage of the original charge was left in the bore after firing.  It appeared, at the time, to relate directly to the temperature of the powder charge when it was ignited.  I should have spent some time looking at that in an experiment where I would fire charges cooled to very low temperatures and then very high temperatures.

I am thinking back to an old paper on an explosion of black powder in a magazine at a mine.  They used to wet the powder up to about 2% moisture to slow it down to give a better "heaving action".  But at the same time the magazine was warm and not vented.  The higher moisture content of the powder caused a chemical reaction in the powder between the sulfur and the potassium nitrate that evolved heat and warmed the powder even more.  Eventually the entire mass of powder reached its ignition temperature and it blew up.  Black powder is said to be incapable of true detonation.  But in this case it mimicked true detonation with devasting results.  So I surmise that with this thing about heat in versus heat out in bp combustion the temperature of the charge has an influence on this ignition and combustion rate.  Simply because with powder combustion you have this relationship between how many calories of heat it take to begin the combustion of the ingredients which then evolves a lot more calories to continue and increase the rate of combustion of a given mass of powder.  The more calories of heat in the powder prior to ignition simply means that less will be required to get it going and keep it going.

I think the only time barrel temperature would come into play was if a charge was loaded and allowed to sit until the powder charge was warmed up to the temperature of the barrel.  Loading a powder charge down a warm or hot barrel does not instantly heat the entire mass of powder to the same temperature as the barrel.

I think this also about covers Dr. Tim Boone's follow-up post.

Any follow-up to this will be spotty.  Yesterday a bike ride until after it got dark.  Tomorrow same deal.  We are seeing very large numbers of deer on our rides.  Four years in Tioga County with a flinter and nothing.  Had I been mounted on a mountain bike with the flinter?  Ye-Ha!!  If you are on a bicycle and rolling very slowly they have utterly no fear of you.  The other evening a herd of 30 to 40 deer in Valley Forge Park had the wife stopped and trapped on the trail for almost 15 minutes.  A nice 6-point buck being in charge at the time.

Bill K.

[Dphariss]

I thought about the barrel temp variation too, when I read that........ a goal of consistency of accuracy would seem to argue for a slow rate of fire (max cooling time) and perhaps regular wiping with a wet patch...... to cool as much as to control amount of fouling???    I wonder how big the variations in powder temp need to be to significantly influence ignition speed and perhaps pressure???

I bet the powder compression does have less effect than commonly believed. verrrryy interesting.

This is generally barrel related not powder related. Some barrels due to the state the material the barrel is made from, how its stocked etc. may shoot better if kept at a uniform temperature. But there are a large number of variables here. How the steel reacts to being heated is the prime factor though
Even modern smokeless powders are less temp sensitive than those of the early years of development.
Some of which were know for pressure spikes in hot climates.
Dan

[Dphariss]

Powder compression does several things. One thing it does in increase load inertia. I also know uniform pressure on the powder will produce more uniform ballistics than haphazard compression. This is a function of load inertia.
Using water based lubes like spit etc or very dry oiled patches will also increase load inertia and some rifles will shoot better as a result. Water soluble oil, mixed with water and then allowed to air dry after the patched are wetted works very well too. Oil like Neatfoot or Sperm Whale oil will work if the patches are squeezed in a vise to remove the excess oil. Water etc and very dry oiled patches are all poorly lubricated and will provide more load inertia. This forces the powder work a little harder and this reduces velocity variations.
The powder does not burn the same loose as it does compacted when in a gun barrel/cartridge case.
Powder that is drop tubed properly, and many serious ML shooters use them, will pack pretty tightly. The compression I use in BPCR is to assure that the powder stays locked in that state, otherwise drop tubed powder can settle more after drop tubed if vibrated for a long time.
A mulitple national Champion in BPCR silhouette found this out the hard way.
He found that his rifle shot best with no compression on the powder, just with the bullet seated to touching it.
HOWEVER. He lived 10+ miles by horse drawn wagon from the road and about 1000 road miles from the Nats.
The powder settled further due to travel, his velocity variation went up and it was not a pleasant Nats for my friend.
A slight amount of compression even 1/32" will lock it in place.

Powder that is uniformly packed will produce better ballistic consistency since the flame spread from shot to shot is nearly the same. Loose powder will not burn the same every time and will foul far more. Both these things will result in accuracy problems. Vertical dispersion can get extreme at longer ranges. I wonder if the radiant heat wave Mad Monk has related is more controlled in a well compacted powder column than in a loose one. (?) I do know that the loose packed powder charge will almost surely cause a low flier. I think the loose powder perhaps ignites faster but does not develop as much energy per gain as compacted powder will.

Someone related that a friend had tried putting "tails" on the balls he shot from a Brown Bess. He reported that it reduced the horizontal dispersion but not the vertical. I would point out that this is likely something mechanical or shooter related. No rear sight made elevation hard to hold or the vent was too large and resulted in velocity variations.

There is far more to BP than just putting it in the gun if you want the gun to do more than just go bang on command. Most ML shooters just are not that serious and they accept accuracy that people in BPCR sports will not.
Most of the people that win serious matches (paper scoring rather than hit or miss novelty matches) do so because they have fully sorted out their rifle and know how to shoot. Most ML shooters are what I would call plinkers and I fall into this myself. But I also shoot against some very serious shooters when I shoot a match so I am being forced into getting my "@#$%/!! in a group" a little more again.
The shooter wanting best accuracy from any BP rifle really needs to sort it out and work at consistent loading in the way that produces the best accuracy because it really does make a difference how the rifle is loaded, how the ball is patched etc etc. This can take a very long time sometimes. A year or experimenting perhaps.
Gotta call my master gunsmith (I am but an apprentice in many ways) and discuss graver sharpening.
Dan

[Leatherbelly]

May I ask a question about ignition?  Is it not the HEAT from the flame that ignites the charge, not the flame itself?

[Larry Pletcher]

May I ask a question about ignition?  Is it not the HEAT from the flame that ignites the charge, not the flame itself?

This has been puzzling to me for some time.  I can (and do) ignite a pan of priming with a red hot wire.  Obviously no flame there.  But we use flame (burning priming powder) to ignite a barrel. 

My thought here is that heat ignites the powder, but flame is the producer or carrier.  I have tried to come up with a way to test this but so far have not.

The hypothesis I suppose could be "there is a wave of 450+ degrees heat traveling in front of the flame front of the ignited powder."  (True or False) When both the heat front and flame front could be supersonic, how does one measure this?
"Heat front" and "flame front" are my terms - don't know what else to use.
Regards,
Pletch

[Dr. Tim-Boone]

Presumably the heat causes the powder to convert to a gaseous state which then succumbs to  spontaneous combustion? Which sets off a chain reaction with the other nearby granules??  maybe it is the heat that ignites the barrel charge, not flame...although???

[Acer Saccharum]

Here is where I try to explain in Flinstonian terms what I think is happening:

Heat will be in the form of infrared light, invisible to the naked eye. It will travel through space until its energy is absorbed through collision with an object, and the energy in the infrared light is then absorbed by the object. Infrared light can be focused, with a parabolic mirror, to provide a more concentrated beam. The pan can be polished to this effect, as well as the underside of the frizzen can be used to reflect the heat waves back into the pan. When the underside of the frizzen is allowed to build up black fouling, this surface will absorb the infrared, slowing down the ignition. So keep your pan and frizzen bright and clean!

I think the flame is the visible result of elements combining at a rapid rate: oxygen, charcoal, saltpeter.

Please feel free to dispel any myths I am tendering.

Tom

[Acer Saccharum]

Tim, I believe it's the HEAT of the sparks that start the ignition of the prime. Then you have combustion. The sparks are hot strips of steel, sheared off the frizzen by the flint.

Now I am about to start making things up, so I will stop before I embarrass myself.

Tom

[Dr. Tim-Boone]

Yes heat of the sparks or the hot wire. in either case it is not flame that ignites the prime........so is it really flame that ignites the barrel charge, or is it heat..... IF heat is infrared light and can be focused, might the exterior cone shape of a touch hole focus it??  What effect does the internal cone have on the infrared light??    Now I am clearly making things up.......So I await the input of the better educated.......