Primer
Definition
The small explosive cup at the base of a cartridge that ignites the propellant. Conventional primers use lead styphnate, barium nitrate and antimony sulphide; lead-free Sintox primers use DDNP, tetrazenes and potassium nitrate.
- Location
- At the base (head) of a cartridge
- Function
- Impact-sensitive explosive charge that ignites propellant when struck by the firing pin
- Conventional composition
- Lead styphnate, barium nitrate, antimony sulphide
- Lead-free alternative
- Sintox primers (DDNP, tetrazenes, potassium nitrate)
Common questions
What does a primer do in a cartridge?+
A primer is a small explosive charge that sits at the base of a cartridge. When the firing pin strikes it, the impact ignites the primer, which then ignites the propellant powder inside the cartridge. This chain reaction propels the bullet forward.
What chemicals are in a typical primer?+
Conventional primers contain lead styphnate, barium nitrate, and antimony sulphide. Lead-free alternatives called Sintox primers use DDNP, tetrazenes, and potassium nitrate instead. These compositions are sensitive to impact but stable enough to survive handling.
Why do forensic scientists care about primers?+
Primers are part of gunshot residue (GSR), which gets deposited on a shooter's hands and clothing. Analyzing primer residue can help connect a person to a fired weapon or establish that a firearm was discharged at a particular scene.
Related terms
- Ammunition
- The cartridge assembly fired by a firearm. Comprises case, primer, propellant and projectile. Defined under Section 2(1)(b) of the Arms Act 1959...
- ASTM E1588
- ASTM International standard practice for gunshot residue analysis by scanning electron microscopy with energy-dispersive spectrometry. Defines particle classification (characteristic, consistent-with, indicative), morphology...
- Bore / Caliber
- Bore is the internal diameter of the barrel. Caliber is that diameter expressed in inches (.32,.38) or millimetres (9 mm, 7.62 mm)....
- Cartridge
- The complete round of ammunition: case plus primer plus propellant plus projectile, assembled as a single unit for breech loading.
- Dermal Nitrate (Paraffin) Test
- Historical test where molten paraffin was cast on the suspect's hand and the cast was sprayed with diphenylamine in sulphuric acid. Blue...
- Firearm
- A barrelled weapon that launches a projectile by the rapid expansion of gas from a confined burning propellant. Includes handguns, rifles and...
- GSR
- Gunshot residue. The mix of particles ejected from a firearm on discharge, composed of primer metals (Pb, Ba, Sb), propellant residues (nitrites,...
- Modified Griess Test
- A contact-transfer colour chemistry test for nitrite-containing propellant combustion residue. Sulphanilic acid undergoes diazotisation with nitrous acid (from NO2 on the target...
- Projectile
- The object expelled from the barrel. Single bullet in rifled arms, multiple pellets or single slug in shotguns.
- Propellant
- The chemical charge that burns rapidly inside the case to generate the gas that drives the projectile down the barrel. Black powder...
- Rifling
- The helical groove pattern cut into a firearm barrel that imparts spin to the bullet, stabilising it in flight. Rifling lands and...
- SEM-EDX
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy. The electron beam excites characteristic X-rays from each element present in the target grain, giving...
Explained in these topics
- Firearms: Types, Classification, Ammunition and CompositionsA small impact-sensitive explosive charge in the head of the cartridge that ignites the propellant when struck by the firing pin. Classical composition is lead...
- Gunshot Residue (GSR) Analysis: Detection MethodsThe small explosive cup at the base of a cartridge that ignites the propellant. Conventional primers use lead styphnate, barium nitrate and antimony sulphide;...