Better Marksmanship Through Chemistry:  How the US Solved the Problem of Metal Fouling in High Power Rifles

US riflery underwent a tremendous change with the advent of the Model 1903 rifle chambered for the Model 1906 .30 caliber cartridge.  A second generation smokeless powder round, the .30-06's performance would be the benchmark for martial and sporting rifles for more than fifty years.  The road wasn't always smooth, and there were several developmental issues to be overcome before the round was truly perfected.  One of the problems encountered was that of metallic fouling in the bore.  This month's technical trivia column explores the various paths that eventually led to the solution of the metallic fouling problem.

UNSIGHTLY LUMPS
With the advent of the second generation of smokeless powder cartridges, typified by the .30-06 and the spitzer tipped variants of the Mauser family (6.5x55mm, 7x57mm, 7.65x54mm, and 7.92x57mm) came the problem of metal fouling.   The new cartridges were much more powerful than their predecessors, and used loads that generated significantly higher chamber pressures and temperatures.  Shortly after their introduction, shooters began to notice what appeared to be lumps near the muzzle end of their barrels.  Try as they might, they could not scrub the bores free of these lumps, and as a result the accuracy of their arms began to degrade.  As it turned out, the lumps were actually composed of cupro-nickel - bullet jacketing material.  As the bullet traveled down the bore, an intense heat was developed as a result of the friction between the bullet and the barrel.  As a result, some of the jacketing material began to adhere to the bore.  The result was cumulative - as soon as the jacketing began to stick to the bore it created a rough spot, which pulled off more of the next jacket, and so on.  The initial treatment was to use something called "Ammonia Dope."

THE (NOT SO) STRAIGHT DOPE
Ammonia Dope was a solution containing ammonia persulphate, ammonium carbonate, and an ammonia/water solution.  In use, the breech of the gun was stoppered, and a tight fitting rubber tube slipped over the muzzle.  In this way, when the barrel was filled to the muzzle with the Ammonia Dope, no part of the steel in contact with the Dope would be exposed to the air.  Should the barrel come into contact with both the Dope and air at the same time, the Dope would corrode the steel and ruin the barrel.  Once filled, the barrel was allowed to stand for twenty minutes, then the solution was drained, and the barrel quickly dried and oiled.  The Dope couldn't be stockpiled, as any other than a fresh mixture would immediately corrode the steel.  Even if all precautions were taken, the Dope would occasionally attack the steel, giving it a sandblasted, rough texture, and rendering the bore useless.  Additionally, should any leak past the stopper, it was liable to get into the action and result in serious rust damage.

Clearly then, Ammonia Dope was not the optimum solution to the problem.  A new theory suggested that in order to prevent metal fouling, some sort of lubricant needed to be interposed between the bullet and the bore.  A number of different types of greases and vaselines were tried, with a variety of supplemental ingredients were used.  To a large extent these did ameliorate the metal fouling problem, and in the period immediately preceding and following the First World War, no well equipped rifleman would think of being without a small pot of grease called "Mobilubricant."  The bullet was dipped into the grease just prior to being chambered.  All seemed to be quiet on the metal fouling front.

GREASE IS NOT THE WORD
Unfortunately, it wasn't.  A series of tests at Frankford Arsenal revealed that the use of grease dangerously increased bolt thrust and chamber pressure.  When a rifle is fired, the case is driven back against the bolt face with the force of the powder pressure minus the resistance generated by the friction of the expanding brass case against the chamber walls.  Grease in the chamber diminishes the amount of friction significantly, and allows  almost the entire rearward thrust to operate on the bolt head.  With respect to pressure, a test was conducted with 1920 National Match ammunition, caliber .30-06, where the chamber pressure of dry ammunition was noted to be 51,355 pounds per square inch.  When the bullet and neck were lubricated with vaseline, the pressure rose to 59,000 pounds per square inch.  When the tests were repeated with the entire case being lubricated, pressure soared to 71,154 pounds per square inch, and destroyed the pressure gauge.  In each case where lubricant was used, it was used sparingly.  Grease had failed to solve the problem.
 

TIN PAN SOLUTIONS
During the First World War, the French had experienced a similar fouling problem from the copper rotating bands on their artillery projectiles.  To prevent the fouling, they had placed strips of tinfoil in the propellant charges.  This was noted by the technical staff at Frankford Arsenal.  In order to apply the necessary tin to the bore of a rifle, it was decided to tin plate the bullets.  A batch of tin plated. bullets were assembled for the 1921 National Matches.  The bullets were .3079" in diameter with a tin plating .0003" thick.   Interestingly, the information card supplied with the ammunition specifically warned against the use of grease with these cartridges, citing that dangerous pressures in excess of 75,000 pounds per square inch could result.

While they seemed to solve the problem of metal fouling, additional experiments had noted some other peculiarities with the new tin plated bullets.  Specifically, the force needed to pull the tin plated bullets from the case ran from 300 to 600 pounds.  This was a far cry from the fifty or sixty pounds that was considered "normal."  What was happening was that the tin on the bullet was bonding with the brass of the case to produce a "cold solder" effect.  In the tests of the tin plated bulleted ammunition, there had been no ill effects observed.  However, the tests were conducted under controlled circumstances in a laboratory environment.  And they had failed to take into account one of the most volatile variables in the equation - the shooter.

A number of rifles were destroyed at the 1921 National Matches.  Examination of the circumstances of each accident indicated that greased cartridges had been involved.  To understand just why these somewhat spectacular results occurred, it is necessary to take a closer look at the interaction between the ammunition, the grease, and the gun.  Smokeless powder burns very quietly when ignited in an open space.  Try it  - pull the bullet from a modern rifle cartridge, dump out the powder onto a fireproof surface, and light it.  You'll get a very quiet, very pretty blaze that quickly dies out.  If, however, it is confined in a very small space, the gas and heat generated cannot escape.  As a result, the burn rate increases which generates more gas and more heat, which in turn increases the burn rate still further.  The cycle continues until an explosion ensues.

With the tin plated ammunition, the bullet was essentially soldered into the neck.  When a cartridge was fired, the first thing that happened was that the initial pressure expanded the case in general and the neck in particular expand, and in doing so, release the bullet from the "soldered" union with the case neck.  The bullet was then free to move down the bore and create room for the expanding volume of powder gas.  However, with a greased bullet or case, the space between the neck of the case and the neck of the chamber was filled with an incompressible substance, and the initial rise in pressure was unable to expand the neck and release the bullet.  As a result, the burning powder was very strongly confined at the beginning of ignition, and the pressure then spiked, with disastrous results.

As a result of the experience gained during the 1921 National Matches, the War Department banned the use of tin plated bullets, and supplies on hand were scrapped.

LUBALOY AND GILDING METAL
While the implementation of tin in the gun, powder, bullet equation had been banned, the concept remained alive and well.  Two other approaches for introducing tin were used extensively.  One of these was the actual incorporation of tin into the propellant, and the other was the use of tin in the jacketing material alloy.  Just such a jacketing material alloy was introduced in 1922 by the Western Cartridge Company under the trade name "Lubaloy," or lubricating alloy.  Lubaloy was an alloy of copper, zinc and tin.  Up to 1922 the standard bullet jacketing alloy had been cupro-nickel coated steel (1893 - 1902), followed by solid cupro-nickel, which was an amalgam of 60% copper and 40% nickel.

Gilding metal, which consisted of 90% copper and 10% zinc, had been used for some commercial cartridges prior to the early 1920's, but was not considered to be stiff or strong enough to withstand the rigors the service bullet was subjected to.  Tests were conducted with Lubaloy (which was basically gilding metal containing about 2% tin) to see if it would suit service needs.  In the event, Lubaloy turned out to be a very suitable jacketing material.  When it was used, the lumpy metal fouling that was the trademark of cupro-nickel clad bullets disappeared entirely.  Lubaloy's first triumph came when the Western Cartridge Company won the contract for the selection of the Palma Match long range ammunition for the 1922 matches.  The ammunition supplied under the contract was called Lubaloy-Palma and used a jacket composed of  90% copper, 8% zinc, and 2% tin.  Interestingly, Western's bullets competed with those supplied by the Frankford Arsenal, which also had gilding metal jackets, and were used in the National Matches.  The gilding metal innovation was nothing short of revolutionary to the shooting community, as this excerpt from the April, 1922 issue of Arms and the Man (antecedent to the American Rifleman) notes:

Perhaps the most important and outstanding feature of the entire test is that gilding metal and bronze have been so improved in process of manufacture that they can now be utilized as materials for jackets of bullets that will give superior accuracy, and that these jacket materials have the great advantage of depositing no lumpy metal fouling in the bore of the rifle.  These Lubaloy and gilding metal jackets are to all intents and purposes practically the same both in composition and result.

Note:  Data for this month's trivia page was gathered from:

Hatcher, Julian S., Hatcher's Notebook,  Stackpole Books (Harrisburg, Pennsylvania, 1966) ISBN 0-8117-0795-4

Hatcher's Notebook is available from Amazon.com.  Click on the image to order:

 
 

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