[Slamfire]

As for the type of lubricant, I am aware the Navy and Army experimented with Teflon coated steel cased ammunition in the 50’s. I think oiled Teflon cases performed best, but the whole thing was more expensive at the time than just using brass cases. I predict the cost of brass will instigate more research into various forms of case lubrication for steel cases. The first use of lubricants on steel cases that I am aware of is the German practice in WW1. They were running out of brass, used steel, and coated 8mm Mauser cases with ceresin wax. Worked so well that only waxed cases were wanted as plain steel cases obviously caused jams.

Modern lubricants are much more advanced than lubricants from 10 years ago. I am aware of lubricants having nano diamonds as additives, there are probably a number of exotic lubricant additives that are inappropriate for use in firearms, and probably cost prohibitive to use as a case lubricant.

As Varmint Al’s analysis shows, there has to be some friction between case and chamber or the case will collapse. To date, plain mineral oil, automotive oils, are incapable of causing such a phenomena. However, in blackpowder guns, probably due to low pressure, but, for whatever reason, the chamber must be kept dry and there must be friction between the case and chamber. Blackpowder shooters report wet cases being pulled up into the barrel!. One BPCR competitor told me some of his cases were dragged up to the throat and had rifling marks. I wonder if the crimp did this.


As to the historical use of oilers, I went to The Machine Gun History, Evolution, and Development of Manual, Automatic, and Airborne Repeating Weapons by George M. Chinn Lieutenant Colonel, USMC VOLUME I OF FIVE VOLUMES

I was surprised to find that case lubricant prevented case head separation in weapons with excessive headspace. This is not a practice I advocate, because I would be concerned with action peening, but evidentially billions of lubricated rounds were fired in mechanisms with excessive headspace.

http://ibiblio.org/hyperwar/USN/ref/MG/I/

Do notice that Major General Hatcher is mentioned on the acknowledgements.

Schwarzlose Machine Gun, 8 mm. page 231

This system is appropriately designated retarded blow-back. Due to the fact that the cartridge is extracted under relatively high gas pressure, it was found necessary to lubricate the ammunition. Schwarzlose settled this problem by installing, as an integral part of the weapon, a pump to lubricate the cases. This device pumped a squirt of oil in the chamber between each extraction and loading. The combination of the lubricated ammunition, heavy spring, large bolt assembly, and short barrel allowed the use of an unlocked action which proved quite satisfactory.

Chapter 16 Revelli Machine Gun --251--

An oil pump for automatic lubrication of each round was an integral part of the receiver.

Chapter 8 Nambu Automatic Weapons page 353


All Nambu machine guns were gas operated and air cooled with many radial fins giving more surface for cooling. The earlier models had rectangular gravity oil reservoirs so that as rounds were fed into the feed opening they engaged a spring-loaded lubricator. This action caused oil to flow through perforations onto the cartridge cases. Such lubrication was needed because manufacturing the components to such close tolerances as to permit a workable head space had not been possible at the time. The oil permitted the cartridges to slip back against the bolt until lock clearance was taken up, thereby eliminating the danger of a ruptured cartridge case


Chapter 9 Revelli Aircraft Machine Gun page 354

The Italian Air Force during World War I was so desperate for an adequate rifle-caliber machine gun of native origin that it ordered the lightening of the water-cooled 1914 model Revelli. This was accomplished by the removal of the water jacket and use of an air-cooled barrel with longitudinal ribs. It not only gave more cooling surface but also strengthened the barrel, cutting down dispersion. The rate of fire was increased by use of ammunition more thoroughly lubricated by means of a built-in oil pump.

Chapter 21 Breda Machine Gun page 416


A large oil reservoir was built into the top of the receiver, directly over the feedway. This lubricator was operated by the recoil and counterrecoil movement of the barrel and barrel extension, squirting oil with each complete cycle on the rounds then being positioned on the floor of the feedway.

Page 419

Like all Italian machine guns oil was used freely on the ammunition since head space was not adjustable on the weapon. The fixed relation between the front face of the breech-lock receiver and the gas port in the barrel made impossible rotation of the barrel in order to advance or retract the chamber for correct head space. The oiling of the ammunition was resorted to in this case in order to compensate for the above condition.


Chapter 29 Sistar Machine Gun page 465

The light machine gun, while having only a 20-shot magazine, did have a feature that the company made great effort to demonstrate on every occasion. The gunner, without rising, could pivot the swinging magazine forward from the prone position and insert in a matter of seconds a fresh supply of loaded rounds directly from the cardboard container into the feed system. By this ease and speed in loading he could keep up practically uninterrupted fire.

The weapon was recoil operated, the barrel having an open jacket that gave it support and a bearing for "floating" the recoiling parts.

A built-in oil pump on the left side of the receiver sprayed a small jet of oil on the incoming rounds as each was positioned for chambering. This device was actuated by the recoil and counter-recoil movement of the barrel extension.

Polsten Cannon page 521

One of the principal differences between the Polish-designed gun, known officially as the Polsten 20-mm Automatic Cannon Mark I, and the original Oerlikon was the built-up receiver of welded construction which had heretofore added greatly to the machining problem in mass production. The Polsten gun was also lighter in weight, but as the weapon was intended for shipboard and ground use, this did not seem of too much importance to the British. It could be fed both by clip or drum magazine, and could only be fired full automatic.


Chinn does not mention that the rounds for the Polsten Cannon were greased but this will be found in Brassey’s “Small Arms” by Allsop and Toomey. In fact, Brasseys Small Arms has a whole section starting page 70 about case lubrication.

The Machine Gun Part V

Chapter 14 Birkigt Type 404 20-mm (Hispano-Suiza) Cannon

--578--
After further comparative tests in late April 1942, it was again definitely decided by the Ordnance Department that all American-made 20-mm automatic guns continue to be made with the chambers longer by one-sixteenth inch than the British regardless of the employment of the same ammunition. This decision was final as far as American production was concerned, but in no way did it change the British representative's view on the longer chamber's performance.
Oddly enough, the question was again raised, not by the English or our many proving grounds, but by manufacturers of 20-mm ammunition. In testing their cartridges for reliability of action, they encountered a series of malfunctions known as light-struck primers that were all out of proportion for such a weapon. These were not isolated cases, the reports coming in from practically every maker of 20-mm ammunition that was engaged in function firing his products.

Since the munitions companies pointed out that the faint strikes were due to lack of impact on the primer resulting from error in the gun, and not as a result of defective materials or workmanship, it was decided to conduct another test on an extensive scale at Aberdeen. Ninety of the 20-mm guns, M1 and AN-M2, selected from every facility producing them, were expended in this test with all types of ammunition, both from accepted and rejected lots.
A complete record was made of every malfunction during the entire test and the probable causes of the trouble. The engineers in charge of the project in the early stages of this test recommended that two modifications should be made to overcome the serious malfunctions:
"(1) Shorten the chamber one-sixteenth inch, thus modifying it to approximately the British chamber.
"(2) Replace the extractor spring with a solid plug, thus positioning the rounds by means of the extractor. This change would include such modifications to the extractor, the bolt, and the ejector, as were deemed necessary."--588—

During war all that can be done is to install and make function as reliably as possible that which is issued. With the mounting of the 20-mm cannon in Navy, planes a series of malfunctions began that could not be properly corrected at the time because manufacture was at the peak of production. The slightest change would practically mean retooling. The most serious problem was the oversize chamber. There still remained considerable variance in dimensions between the chambers of the British and American cannon, even after the latter chamber was made one thirty-second inch shorter


Due to an outmoded agreement of long standing, everything above caliber .60 in the Army is considered artillery and the manufacture of the Hispano-Suiza cannon therefore came under this classification. In other words the production of this high-speed machine gun was done under artillery manufacturing tolerances. The resulting poor mating of parts, coupled with the inherent fault of all gas-operated weapons whereby the breech locking key in the receiver is immovable and the position of the gas port in the barrel is permanently fixed, made it impossible to adjust the relationship between barrel and breech lock to establish head space. Thus the most vital measurement in any automatic weapon was governed by chance in this instance.

An unfortunate discovery was that chamber errors in the gun could be corrected for the moment by covering the ammunition case with a heavy lubricant. If the chamber was oversize, it served as a fluid fit to make up the deficiency and, if unsafe head space existed that would result in case rupture if ammunition was fired dry, then the lubricant allowed the cartridge case to slip back at the start of pressure build up, to take up the slack between the breech lock and the breech lock key. Had this method of "quick fix" not been possible, the Navy would have long ago recognized the seriousness of the situation. In fact, this inexcusable method of correction was in use so long that it was becoming accepted as a satisfactory solution of a necessary nuisance.