Pressure Testing

The American National Standards Institute/Sporting Arms and Ammunition Manufacturers Institute recognizes two methods for pressure testing of small arms ammunition. These are with Copper Units of Pressure (CUP) and Piezo (PSI). Accurate Arms Company uses both methods.

The standards for pressure used by Accurate Arms Company in preparing this manual are contained in ANSI/SAAMI Z299.3-1990 and Z299.4-1992. All maximum loads are kept equal to or less than the Maximum Average Pressure as defined in the respective manual.

Accurate testing with C.U.P. is done in two methods. In the first the pressure is read off the case mouth. In the second the pressure is read through the case wall. The basic principle of measuring pressure with the copper crusher is to place a copper cylinder or crusher on top of the piston in the pressure barrel. The piston is protected on the bottom by a gas check and lubricated with non-detergent oil. The anvil screw holds the crusher firmly on top of the piston during firing. After firing the crusher is removed and measured with a micrometer. The degree of compression is converted to a pressure (C.U.P.) by means of a tarage table which is provided by the manufacturer for each lot of crusher.

Accurate testing in Piezo is also done by two methods. The first is through the use of a conformal transducer. This is the fastest and easiest method to use. A pressure barrel is fitted with a transducer whose diaphragm is contoured to conform to the outside of the cartridge case. The pressure applied to the diaphragm is read as P.S.I.. When this pressure is added to the offset pressure established for that lot of case you have the total pressure produced by that load. The offset is the amount of hydraulic pressure required to begin expansion of the brass case. This results in one of the drawbacks of this system. Only new cases can be used and they must be calibrated lot by lot for accurate pressure reading.

The other method of reading pressure in Piezo used by Accurate is derived from military small arms ammo testing procedures. A force transducer is used in lieu of the copper crusher in conjunction with a piston type barrel. When using this method a hole is drilled in the case allowing the gas to impinge directly on the gas check protecting the bottom of the piston. The voltage produced by the force transducer is read directly as Pounds per Square Inch (P.S.I.) on a peak meter. This method is especially useful in working with wildcats.

The pressures and velocities produced in all test methods are calibrated using SAAMI Reference ammo if available. If not, then factory ammo (if available) is fired and used to determine the pressure limit. In the case of a wildcat cartridge a pressure limit was selected using the most similar factory cartridge.

Every effort has been made at Accurate to provide safe, trouble-free, loads. Please feel free to contact our technical department if you have any questions regarding any of the loading data in this manual.

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Responses

  • ESTHER
    What companies will pressure test handloads?
    4 years ago

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