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Old September 7, 2012, 08:44 PM   #10
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Join Date: May 27, 2007
Posts: 5,081
I found an ancient report on lubricated 20mm cannon cases, which incidentally put out a lot more bolt thrust than any 30 cal case, here.

I cut and pasted extracts from the report.


In the past decade tests at the Naval Proving Ground had always demonstrated that waxed ammunition was unsatisfactory. Also, it was known that the Army and Air Force had frequently encountered storage and service problems caused by the use of wax on 20MM brass ammunition. Therefore, naval procurement of Army manufactured M21A1 brass ammunition had excluded wax coatings for 20MM cartridge lubrication. Since early in the Korean War it has been naval practice to oil cartridges just prior to use '(reference -(a)).

Research at this Laboratory on dry film lubricants for cartridges, began in September 1950. In references (b) and (c), were listed the guides which were to be used in determining the value of a dry lubricant coating for ammunition.

The most important conclusion of that investigation was that a thin film of polytetrafluoroethylene (Teflon) was the most satisfactory dry lubricant coating for cartridges. This conclusion was confirmed in the NRL reports of references (d), (e), (f), (g), (h), (i), and (J).

In the past either ceresin wax or microcrystalline wax had been used by the Army as cartridge lubricants. Ammunition storage difficulties with ceresin wax films led the Frankford Arsenal to use a higher melting point microcrystalline wax as an outer coat over the "Case-Cote" varnish.

Since the use of light oil coatings over Teflon-coated guns has a beneficial effect on rate of fire, it was necessary to repeat the firing tests previously performed on all test ammunition. This resulted in a significant increase in the rates of fire. Thus, oiled brass cartridges averaged 789 rpm, oiled bare steel cartridges averaged 789 rpm, "Case-Cote" wax-lubricated cartridges averaged 820 rpm and Teflon-coated cartridges 810 rpm. However, it should be noted that these high rates of fire are not obtainable on a bare steel gun with oil. It was reported in reference (1) that oil on a Teflon coated gun with properly lubricated ammunition usually produces rates of fire 40-75 rpm higher than normal.
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