There is international concern about the amount of airborne toxic materials found in shooting ranges, particularly airborne lead. The Federal Government of West Germany has set the maximum permissible work-place concentration of lead dust at 0.1 mg of lead per cubic meter of air. During tests at German and non-German shooting ranges, equipped with various types of ventilation systems, concentrations of up to 9 mg of lead per cubic meter were measured over exposures of 4-6 hours when conventional, fully jacketed 9.times.19 mm Luger (parabellum) ammunition was used. This high airborne lead concentration is also found in some indoor shooting ranges using .22 caliber rimfire ammunition. The main problem is thought to come from the lead styphnate and barium nitrate used in the priming composition.
One attempt to solve the above problem for centerfire ammunition (which has a primer placed in the center of the cartridge base) has been the "Sintox" primer developed by Dynamit Nobel of Troisdorf, West Germany which is thought to use an amorphous dinol initiating explosive mixed with zinc and titanium compounds rather than lead or barium compounds. However, that priming composition is not suitable for priming rimfire cartridges because it is a centerfire priming mix which does not have enough sensitivity for use as a rimfire priming mix and because it does not easily flow into the rim of the cartridge during the priming procedure. Dinol-based priming mix having a smaller crystalline size than that of the "Sintox" primer was made and was tried by applicant's predecessors at Olin Corporation about 40 years ago, but that mix contained lead in forms of lead thiocyanate and lead peroxide and is thus not suitable as a lead-free primer mix.
A solution to this problem of needing a lead-free, non-toxic .22 caliber rimfire primer has been long sought after. Rimfires have been in existence for many, many years without such a primer having been found. It is well known that rimfire priming mixes must have a sensitivity which is considerably lower than that required by centerfire primers, so even if a low sensitivity lead-free centerfire primer mix is found, it is not obvious how to make a high sensitivity lead-free, non-corrosive, non-toxic rimfire priming mix. The problem is such that the U.S. Government's Army Research and Development Center issued a contract to Olin Corporation to study the feasibility of developing such a primer.
A solution to the above problem is achieved by the present invention which provides a priming composition for use in rimfire cartridges, which composition consists essentially of dinol, manganese dioxide, tetrazene and glass. It is believed that manganese dioxide has never before been used as an oxidizer in ammunition primers, and especially not in rimfire cartridges.