Smokeless powder is the propellant used in the propelling charges for Navy gun ammunition. It is a uniform ether-alcohol colloid of purified NC to which is added a small quantity of diphenylamine or ethyl centrality to assist in preserving the stability of the powder. Smokeless powder is basically unstable since it contains NC and two volatile substances-ether and alcohol. Its length of usefulness depends largely on the conditions under which it is stowed. Moisture or heat speeds its deterioration; a combination of the two has extremely damaging effects.
Classification of Smokeless Powder
Smokeless powder is classified into two types: single-base and multibase.
SINGLE-BASE POWDER.- Single-base powder consists of colloided NC with other materials added to obtain suitable form, burning character, and stability. Several single-base propellants are in use today.
MULTIBASE POWDER.- Multibase powder uses NG and/or NQ in addition to NC as explosive ingredients. Such propellants are commonly called double-base (NC and NG) and triple-base (NC, NG, and NQ). One double-base and one triple-base propellant are in use today.
Index of Smokeless Powder
Smokeless powder types are assigned class designation letters that designate the chemical makeup of the powder as follows:
SP -Smokeless powder
C -Stabilized by ethyl centrality D - Stabilized by diphenylamine
F -Flashless powder
G - Includes nitroglycerine and nitroguanidine
N - Nonhygroscopic
W - Reworked by grinding
X -Water-drying process
These letters are followed by a number that indicates the sequence of manufacture. The combination of the letters and the number is termed the index or the lot of the powder. The combinations of the class designation letters are described below.
SPC.- SPC is a cool-burning, single-base smokeless powder (SP) with ethyl centrality (C) as a stabilizer.
SPCF.- SPCF is a single-base smokeless powder similar to SPC type of powder but containing a flash suppressor to render the powder flashless. SPCF is
found in all 5"/54 universal charge, full-service propelling charges.
SPCG.- SPCG is a multibase smokeless powder stabilized with ethyl centrality and includes NG and NQ in its composition. Although the designation letter for flashless powder (F) is not used, SPCG is a flashless powder.
SPD.- SPD is a single-base smokeless powder stabilized with diphenylamine.
SPDB.- SPDB is a blend of diphenylaminestabilized powders of different lots. The purpose of blending is to provide a uniform index of ample size and desired character from smaller remnant lots.
SPDF.- SPDF is a diphenylamine-stabilized smokeless powder to which a flash inhibitor, such as potassium sulfate, has been added.
SPDN.- SPDN is a diphenylamine-stabilized smokeless powder to which nonvolatile materials are added to reduce the' hydroscopic tendencies of the propellant. The N stands for nonhygroscopic.
SPDX.- SPDX is a diphenylamine-stabilized smokeless powder that is water-dried. In the water-drying process, the powder is seasoned in tanks of warm water to remove volatile solvents, followed by a brief period of air drying.
SPWF.- SPWF is a flashless powder made by the reworking of ordinary nonflashless powder.
M-6 and M-6+2.-M-6 and M-6+2 propellant designations equate to the SPDN and SPDF (respectively) descriptions previously provided. These designations are used to describe the propellants used in 76-mm ammunition. The +2 refers to a 2% mixture of potassium sulfate.