<prompt> FG, FFG, FFFG...used to describe -PrimerCaridgeBlack gunpowderBase of firearms  <response>: the synopsis of forensic medicine toxicology ; Dr k.s narayan reddy ; 28th edition ; Pg.no. 125 ; Black powder is designated as FG,FFG,FFFGetc depending on the size of grains . The more number of F the finer are the grains faster is the burning . 