# Chemical Analysis of Gunpowder and Gunshot Residues
## 2 Main Components of Gunpowder and Gunshot Residue  
The most common type of ammunition currently in use is single-use cartridges, which contain, in a single case, the primer, the propellant, and the projectile (Figure 1) [8; 19; 20]. Depending on the percussion method, ammunition types are distinguished in rimfire and centrefire cartridges. The former is used primarily on.22 calibre cartridges and the latter in higher calibres [6].  
The weapon's discharge occurs when the trigger is pulled, followed by a series of mechanical interactions that release the firing pin, which impacts direct or indirectly with the base rim or centre of the cartridge and ignites the primer [21]. This ignition deflagrates the propellant, rapidly generating a large volume of gases that thrust the projectile through its trajectory [19].  
The primer currently found in most ammunition consists of a mixture of highly sensitive explosives [6] and other compounds, such as fuel, sensitiers, and oxidisers [19]. In modern primers, the primary explosive is lead styphnate, with barium nitrate as the primary oxidiser [6; 19]. The main propellant currently used is smokeless gunpowder (SG), which is characterised by its high burning efficiency, high volume of gas production,  
Figure 1: Schematical representation of a standard “rimfire”.22 cartridge on the left and a standard “centrefire” ammunition on the right.  
low amount of smoke and low amount of debris produced with its deflagration [5; 19]. The primary explosive used in SG can be single-based (containing only nitrocellulose (NC)), double-based (containing NC and nitroglycerine (NG)), or triple-based explosive (containing NC, NG, and nitroguanidine (NQ)) [15; 16; 19; 22; 23]. The former is the most common type of explosive, whereas the latter is used primarily in military calibre ammunition [16; 24]. In addition to the primary explosive, SG can have other components, such as stabilisers, plasticisers, coolants, surface lubricants, flash inhibitors, and sensitiers [5; 19; 22; 25; 26; 27; 28]. These compounds significantly change the chemical and physical properties of the gunpowder and allow it to perform according to the specific purpose for which it was designed [15; 25; 26; 27; 28].  
GSR, also known as cartridge discharge residue (CDR) or firearm discharge residue (FDR) [12; 20], usually consists of burnt and partially burnt fragments from the primer and propellant as well as particles from the cartridge case and the firearm itself [16; 20; 29; 30; 31; 32]. These residues escape through the firearm's openings after discharge and can deposit on the hands and clothes of the shooter, clothes of the victim, or nearby surfaces. However, some of the particles stay inside the cartridges and barrel of the gun [33; 34; 35]. Due to the chemical complexity of the primers and propellants, these residues are complex and heterogeneous mixtures of compounds.  
Interestingly, it is precisely the chemical complexity of propellant and primer formulations currently in use, and consequently of the SG and GSR, that allows their discriminative analysis, which assists in the investigation in the context of forensic analysis [16; 26; 35].