This is a small brass stamping like a shallow mini-tripod, its tip pointing backwards towards the priming pellet and its ‘feet’ facing the open end, therefore the bottom of the primer pocket in the case. Finally, a two or three-legged ‘anvil’ sits on top of everything at the ‘open end’.
There may then be a wafer-thin treated paper covering above the pellet to stop moisture ingress, optional as most manufacturers now use some sort of paint or lacquer sealant. The smallest rimfire cartridges such as ‘bulleted caps’ use primer energy alone in fact, as do modified centrefire revolver cases loaded with wax or nylon projectiles for indoor pistol shooting. (The priming charge’s energy is large enough to account for a significant percentage of the humble. Any such differences shouldn’t be large enough to induce failure or ‘blanking’ with any reasonable pressure load but can and do make ‘reading fired primer condition’ potentially misleading.Īnyway, moving inwards from the closed end, we have an explosive pellet weighing around 1 grain that produces a high-velocity, high-energy stream of hot gas laced with tiny incandescent particles to get the cartridge’s main propellant charge burning and which also adds to its total energy content. Undoubtedly though, there are hardness variations depending on the brass alloy mix, seeing some makes ‘harder’ or ‘softer’ than others and, there are likely lot-induced variations too. Many shooters wrongly believe that BR or magnum models have thicker brass and are therefore ‘tougher’ than standard models, but whilst true for SR types, there are no such differences here. ‘Berdan’ and ‘Boxer’ layouts and primer components. Large rifle primers all come with one brass thickness, a nominal 0.027” (unlike small rifle primers which vary from 0.020” to 0.025” depending on make/type). The first is the brass cup, always brass despite there being ‘silver’ and ‘gold’ coloured examples out there, the former being lightly nickel plated. 1), you’ll see that Boxer-type primers consist of three, sometimes four components. If you look at a sectioned drawing of the beast (fig. Returning to you and me, one of the easiest ways of producing inconsistent ammunition is to make a hash of seating the little beggar in its pocket. Same thing if the flash-hole exit still has brass shards attached from when it was punched through the case-web during manufacture, or is left partially blocked by such brass debris. If the diameter varies significantly within a batch of cases, so will the cartridges’ performance – this showing up in a large MV spread.
Take that little hole that the primer’s eject passes through to get at the ignition charge, nominally 2mm (0.078”) diameter in most cartridges, 1.5mm (0.059”) in a few – the 220 Russian/PPCs, BR family, 6.5X47mm Lapua, and 308 Win Lapua ‘Palma’. The consistency and condition of the primer-pocket in the case-head, flash-hole and of course, mechanical aspects of the firearm (firing pin energy and protrusion) affect performance, sometimes severely.
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An interesting issue is that of matching primer-type and powder in extreme cold conditions, some combinations needing magnum types for 100% reliability and full pressures/velocities.Įven when the primer is superbly made and its specification well matched to the cartridge and propellant, it is only one part of the cartridge ignition system. The last named very rarely occurs, although an occasional ‘bad lot’ turns up.
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