Overview of SALW Marking Methods
Stamping is the most commonly used technique for marking metal. It involves marking the metal part of the firearm by applying pressure on a mould or matrix bearing the marking to be engraved (indenting), inducing a permanent plastic deformation of the crystalline structure of the material. When the stamping technique is used the crystalline structure of the material that is stamped can actually be altered to a depth six times greater than that of the stamp itself. If someone erases the stamped marking on the surface of the weapon, there can still be a legible trace of the marking in the metal itself. These changes in the physical properties of the material can then be used to help restore the markings if they are erased at the surface. Erased stamped markings can be retrieved in about 1/3 of cases thanks to the deep deformations of the metallic structure. Applying a marking using a stamping procedure requires a flat surface. If the surface is uneven or is made of very hard material, a more sophisticated micro-percussion process is used (sometimes computer-guided). This process, also called pin stamping can be used both for plastic and metal surfaces. Characters can be applied at a rate of 1 to 5 characters per second from 1 to 80mm size and at different depths. The potential fragility of some parts can limit the use of this process. Stamping cannot be utilized on plastic and composite materials that are increasingly being used in the manufacture of new generation weapons. In addition, due to its primary applicability to unhardened metals, low-tech stamping machinery is also largely unsuitable for the application of post-production markings. When the parts and components of a firearm have already been manufactured, marking is usually carried out with a technique other than stamping to avoid any damage to the manufactured part.
The casting method adds markings directly to the moulds used to manufacture weapon parts. Casting is also used for plastic and composite materials (injection moulds) on which stamping would be impractical. This method remains in limited use, mainly because of the small surface areas available on some weapon parts. Casting is not suitable for marking serial numbers, which need to be unique for each weapon.
This technique for marking firearms is fairly widely used. Marking is undertaken by removing metal through direct contact with the material. It can also be achieved through Electrical Discharge Machining where the surface layer is heated and vaporized by a continuous electrical discharge. Hardened materials can be marked using this method when traditional techniques such as stamping would be ineffective. However, there can be physical limitations when engraving information on certain surfaces and materials, such as composite materials. This method is also difficult as far as accessibility and resistance of the parts to be marked are concerned, especially if markings are required once the weapon has been assembled.
Laser (Light Amplification by Stimulated Emission of Radiation) permits marking of all kinds of surfaces through burning by oxidization and has the advantage of requiring no physical contact with the surface to be marked. It also enables marking of areas inaccessible to other marking procedures, as well as marking of fragile parts where attempts to remove the mark would render the weapon inoperable. It can be used for composite materials or plastics as well as hardened metals that cannot be marked by classical methods such as stamping. Lasers can mark miniscule surfaces with precision, for example surfaces smaller than 1mm2 and can contain information either in matrix (data matrix) or bar code format. It is also the most practical method to mark logos, text and numbers on a confined space. The disadvantage of laser engraving is that, if the marking is erased, there is no possibility of recovering it.
In contrast to stamping and mechanical engraving, laser engraving is considerably more time- and resource-efficient. Further, laser marks can be applied to virtually all materials and at any stage of the production process, including at post- production stages. Computer-operated lasers can also be used to mark individual rounds of ammunition and the laser marking process can be integrated into the packaging machinery for ammunition. The ammunition can be marked in the cartridge’s groove just prior to being packaged.
Laser marking can be reinforced by sensitizing the surface of the weapon component to be marked to a certain wavelength by using a special product. Information is then marked on the weapon with a laser. The marking is then covered with a layer of paint or a galvanizing product which renders the marking invisible to the naked eye. However the marking is visible when viewed under certain lighting (i.e. infrared or ultraviolet) according to the wavelength for which the surface has been sensitized.
Radio Frequency Identification
Radio Frequency Identification (RFID) uses an electronic chip embedded in a weapon that carries information about the weapon. These electronic chips can be read from a certain distance using an RFID reader and, if needed, information on the chip can be modified.
With electro-chemical methods, an applicator moistened with an electrolyte solution that is connected to an electrical source is placed on a stencil bearing the marking. The stencil is then placed on the surface to be marked. The depth of the marking is regulated with the strength of the electrical current. This method is used on fragile parts of a firearm or certain types of ammunition that will not allow deeper markings. The disadvantage of this type of marking is that if the marking is obliterated, it is unlikely that it could be recovered. In addition, this type of marking is only possible on conductive materials.
Micro-stamping allows for the marking of a weapon’s make, model and serial number (or other identifying information) onto a round of ammunition each time a weapon is fired. Markings are applied to the primer and cartridge case of the round of ammunition by laser engravings on the tip of the firing pin and on the breech face, respectively. Spent cartridges are thus imprinted with identifying information of the weapon that fired it.
Additional marking methods currently used in other sectors are being studied for potential use in marking firearms. Chemical tracers can be added to metal and plastics used for the production of firearms components and ammunition powder. Crystallographic and radioactive elements can also be used to mark weapons and ammunition powder. Colorimetric methods permit the use of tracers that are composed of a set of colour layers, to which a fluorescent layer is added for detection. The observed colour sequence represents a unique numeric code for each manufacturer.