Douglas Stainless barrels?

[Mad Monk]

Goo,

With a charge of 3F in a patched ball gun the powder charge is totally consumed by the time the ball has moved about 3 inches from its initial point of rest.  With a charge of 2F the distance is about 6 inches.



  A can of powder that gave me 2.5% of the original charge as bore fouling at 40 degrees ambient temperature gave me 15% of the original charge weight at 90 degrees ambient temperature.  Under the microscope I could see where the particles had been fused together.  The mass under the microscope looked like a bunch of glass beads joined together in groups.

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I find this fascinating I am especially pleased to know the powder is consumed within such a small distance as three to six inches depending upon the coarseness of the powder.   As far as the ratio of residue and temperature is it due to humidy?     Assuming cold air holds less moisture than warm ?   

In theory 55% of the weight of the original charge would be  a solids after powder combustion.  That means for every 100 grains weight charged you may expect to get 55 grains as solids after combustion.  A cool temperatures these solids are found as individual minute particles.  But as the ambient air temperature goes up these minute particles are heated to the point where they begin to stick together and fuse together into larger particles.  The primary solid product of combustion is potassium carbonate, or potash.  It will melt around 1600 degrees C.  When the powder burns in a small space you may see gas temperatures high enough to melt the potash.

As these solid particle fuse together and grow in size the cannot be suspended in the hot gases and settle out onto the bore walls.  You then eject less of the residue out into the atmosphere with the spent propelling gases when the projectile leaves the muzzle.


I looked at this when I checked one brand of powder versus another in bore fouling.  It started when I shot a lot of GOEX on a cool day.  Temps down around 40 in a morning at the range.  Two weeks later I had this same can of powder at the range on an afternoon when the temperature hit 85 degrees.  I was puzzled.  The cool day gave me no bore fouling problems.  It gave only light fouling in the bore.  Then the next time I used it I had this mass of gooy tar in the bore that took a bunch of wet patches to remove.  So I used some bore diameter brass tubing and made a scraper cup to recover the bore fouling and look at it under a microscope. 
Then suddenly I understood why some bp cartridge shooters in Southern California take their loaded cartridges to shoots in coolers with  cold packs.  Removing the rounds to be fired only before they go up to the line to fire a string of shots.  I never went any further in the work to see if keeping my ML loads cold before shooting on hot days would get rid of the tar problem.

[Goo]

I will have to try this I am hoping to go tomorrow.    I will try cold loads and I will put some loads next to silica gel packs to see if reducing moisture has any effect.

[Mad Monk]

I will have to try this I am hoping to go tomorrow.    I will try cold loads and I will put some loads next to silica gel packs to see if reducing moisture has any effect.

You may not see any change with the silca gel desiccant with the powder.

You sometimes see it written that black powder is hygroscopic.  How much so depends largely on the purity of the potassium nitrate used to make it.  With a high purity potassium nitrate it will only pick up fractions of a percent in weight as the humidity rises.  Then at about 90 to 92% relative humidity the increase will be a bit higher.  All of the bp we now use is manufactured with a good high purity potassium nitrate.

Black powder does not show any moisture increase effect until the moisture content of the powder goes above 1%.  At about 1.5% moisture content the ease of ignition begins to suffer and the burn rates will be slowed.  Most of the brands of black powder we shoot are packaged at the plant with about .5% moisture content.

Even at high humidity the amount of air trapped between the grains of powder in the charge does not contain enough water to seriously effect the combustion of the powder.

This affinity for moisture in the potassium nitrate was once used as a quality control test by C&H in their powder production.  A weighed sample of the potassium nitrate to be tested was placed in a humidity chamber on a scale.  As the humidity in the cabinet was raised they would record the increase in weight of the sample being tested. They watched for the 92% critical point in RH where the sample would then begin to gain weight rapidly.  At 99 to 100% Rh the maximum weight gain allowed would be 1.6%. 

Relative humidity can come into play shortly after the gun has been fired.  Swiss powder is the only one on the market that produces water as a product of combustion.  All of the other brands "burn dry".  That is to say water is not a product of combustion.
But when you fire the gun and the spent propelling gases leave the muzzle there is an inrush of air from outside the barrel.  If that air is high RH the moisture in the air is quickly transferred to the fouling left in the bore.  Depending on the weather if you let the fired gun sit without swabbing you can see a good deal of moisture picked up by the bore fouling.

All of my work suggested that high ambient temperatures are a bigger problem with bore fouling than the relative humidity.

I quit working on that project before I had looked at everything I wanted to look at.  The thing about the same can of powder looking like two different powders when shot under different ambient temperatures needed just a bit more work to better define.

I had once read that potassium nitrate is used in propellant grades of black powder to insure uniform ballistics in the gun.  The comments stated that the manner in which the potassium nitrate breaks down and releases oxygen was the key in this uniform ballistics.  You must heat the potassium nitrate to it's melting point.  Then continue to heat it until it reaches its decomposition temperature where it releases oxygen to support additional powder combustion.  So what happens here is that the powder becomes sensitive to any heat lost to the surroundings during powder combustion.  The burn rate of the powder then can be effected by the surroundings if heat is taken away from the burning powder.  This is why open trains of black powder burn only slowly while closed tube burning can see flame spread rates of 2,000 fps.  So if a charge of powder, in the bore, is hot that will simply raise the temperature of the gases produced during powder combustion.  This is seen in some instances where you have a thin film, or skin,  of a glass-like deposit in the bore just in front of where the ball sat on the charge.  This skin is potassium carbonate that was heated to its melting point and then cooled.  The skin is highly soluble in water but as a film it is slower to dissolve and takes a lot more work with a wet swab than the fine particle deposits would require.