Propellants in Firearms Explained | Forensic Ballistics Notes

 What are Propellants ?

Define : propellant means an agent, which fires the projectiles out from a firearm.

In order to propel a bullet or shotgun charge through the barrel & air, a certainamount of force is necessary. The powder charge gets ignited through primer and converts it in to gas very quickly, thereby resulting in development of high pressure in the cartridge and forcing the bullet to get out of the barrel. The three types of propellants used are : 

(a) Gunpowder (Black powder) 

(b) Smokeless powder 

 (c) Semi- smokeless powder 

   Gun Powder  

• Gun powder is the oldest recorded propellant and had been invented by Chinese around the tenth century.It was used for giving signals and fireworks.
• The gun powder consists of potassium nitrate, sulphur and charcoal roughly in the proportion of 75:15:10.
• The powder is not suitable for high velocity ammunition, as large amounts of powder are required for getting high velocities for the projectiles.
• The powder leaves a considerable amount of solid residue, which tends to foul the barrel.
• It remains fairly stable, if kept dry, over prolonged period.
• It is glazed and polished to increase its storing or keeping qualities.Gunpowder causes much smoke and fouling of the target
• It is mostly used in muzzle loading and blank cartridges
• The powder is available with different grain sizes- from mesh limit 6-10 to 46-60. 

Smokeless Powder   

• The modern high velocity era started with the use of smokeless powders. The basic constituents of the smokeless powders are nitroglycerin and nitrocellulose (gun cotton).
• Nitrocellulose is either used alone or in combination with nitroglycerin to form propellants, the latter are called double based powders, while the former is known as single base powder.
• Some of the double based powders that are commonly used contains Nitroglycerin
• Nitrocellulose and Mineral Jelly are Cordite, modified cordite and Ballistite. The composition of common double based powder is detailed below: 
•  Cordite has 58% Nitroglycerine, 37% Nitrocellulose and 5% Mineral Jelly

Semi Smokeless Powder

Semi smokeless powder is mixture of black powder and nitro cellulose. The approximate composition of the powder is as follows: 

Nitrated wood cellulose  20% 

Potassium nitrate  60%

Carbon  12%

Sulphur  8% 

This powder produces less smoke than gun powder but mixing process is quite dangerous. Thisaspect has prevented its extensive production and use. 

RDX Based Propellant 

A new propellant is which the active ingredient is from the family of Cyclo-tri-methylene-triamine (RDX) has come up. It is being utilized in the manufacture of cartridges by controlling not only the shattering nature of the high explosive butalso its heat production. The advantages are obvious. The rate of fire can be increased without detrimental effect on the weapon firing the ammunition. However its composition and other details are not available presently.

Suggested Readings: 

Classification of Firearms & Ammunation

History and Devlopment of Firearm 

Parts of a Firearm: Complete Guide with Diagram