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A closely guarded (and patented) secret, this new Eleyprime process had two huge consequences: It eliminated the risk of explosion from the preparation and dispensing of priming compounds, and it allowed the amount of priming material applied to each individual rimfire case to be very tightly controlled in a normal workshop environment using automatic equipment.
This last part is critical because it has long been known that case-to-case variation in the amount of priming material is the most important factor regarding variations in .22 LR rimfire performance. This is due to the fact that in small rimfire cartridges the primer is a significant portion of the actual propelling charge (much more so than in larger centerfire cartridges) and because conventional priming compound is too sensitive to be aggressively metered and applied.
The Eleyprime System allows exactly identical amounts of the inert powder to be put in each case. Then a round-tip rod is inserted down into the case to press the powder evenly into, and around, the rim, and a single, metered drop of water is added, which activates the compound over a several-hour period.
After drying, the cases can then be conventionally charged with precisely metered propellant (five rounds at a time on the TenEx loaders). Before Eleyprime, there was an average 31 to 39 milligram spread in the amount of priming material round-to-round in TenEx ammunition. With the Eleyprime System (EPS), the spread was reduced to only plus/minus 1.0 milligram. It was a stunning achievement, and in 1988 Eley received the prestigious Queen’s Award for Technological Achievement.