FG, FFG, FFFG... used to describe

    A. Primer

    B. Cartridge

    C. Black gunpowder

    D. Base of firearms.

Answer: C. Black gunpowder.

Explanation:

Black gunpowder: 1. It consists of potassium nitrate(75%); charcoal(15%) and sulphur(10%).

                             2. It is designated as FG, FFG, FFFG, etc., depending on the size of the grains. 

                                 The more number of F's , the finer are the grains and the faster in burning.

                             3. One gram of powder produces 3,000 to 4,500 c.c. of gas.

                             4. The gas consists of CO, CO2, Nitrogen, Hydrogen sulphide, Hydrogen,

                                 Methane, etc.,all at a very high temperature.

Smokeless powder: 1. It consists of nitrocellulose(gun cotton)  ~ single base (or)

                                                     nitrocellulose+nitroglycerine  ~ double base (or)

                                                     nitrocellulose+nitroglycerine+nitroguanidine  ~ triple base.

                              2. Triple based powder is commonly used.

                              3. They produce much less flame and smoke and are more completely burnt 

                                 than black powder.

                              4. One gram produces 12.000 to 13,000 c.c. of gas.

Semi-smokeless powder:  is a mixture of 80% of black and 20% of the smokeless type.

                            

Ref: Narayan Reddy's 'The Essentials of Forensic Medicine and Toxicology', 33rd edition, p 214.