Measuring and testing – Ordnance and projectile
Reexamination Certificate
2001-02-09
2002-05-14
Raevis, Robert (Department: 2856)
Measuring and testing
Ordnance and projectile
Reexamination Certificate
active
06386028
ABSTRACT:
RELATED APPLICATIONS
The present application is based on, and claims foreign priority benefits of Great Britain application number 0002901.7, which was filed on Feb. 10, 2000.
The present invention relates to a method and apparatus for measuring the pressure in a firearm during discharge thereof.
To date a large variety of methods and apparatus have been used to measure and/or calculate the peak chamber pressure within a firing chamber of a firearm when it is being discharged to fire off a bullet or other projectile. Measurement of chamber pressure allows for example a custom-made ammunition “load” (or hand load) to be compared with a factory-made load. It also allows the development of accurate hand loads by measuring the pressure uniformity generated within a firing chamber and or to measure the temperature sensitivity of loads in order to avoid problems with temperature extremes and to maintain the accuracy or even to assist in choosing the best powder for a given application by determining the efficiency, pressure uniformity and temperature stability. These factors are a few among the many for which it is generally necessary to measure chamber pressure.
Furthermore, where custom-made ammunition is to be used, measurement of the peak chamber pressure is advisable to ensure that the load is not too “hot” i.e. creates excessive chamber pressures which would seriously reduce the life-time of the barrel of the firearm, in addition to increasing the risk of a catastrophic failure of the barrel through excessive forces being exerted therein.
The custom manufacture of ammunition or hand loading is a relatively cheap method of obtaining ammunition and offers a wide variety of combinations of casings, powders and bullets which may not otherwise be available e.g. as a commercial product. As previously mentioned, it is generally considered good practice, in addition to considering the safety aspect, to ensure that the load is not too “hot”. This can be done by measuring the chamber pressure during discharge of the firearm firing off a sample.
Prior art devices for measuring and/or deriving the chamber pressure include the well-known “Powley P Max” device as marketed by Homer Powley in the 1960's. The Powley P Max device generally takes the form of a tube which is attached to a rifle using the mountings normally provided for attachment of telescopic sights thereto. A freely movable weight of known mass is located adjacent a crushable lead disc fixed within the tube. Upon discharge of the rifle, the rifle, the tube and the crushable lead disc therein all recoil. The freely movable weight, however, tends to remains stationary and crushes the lead disc within the tube as the recoiling lead disc is driven against the weight. The crushable lead disc is calibrated to allow a user to derive the force (peak pressure) which has acted upon the lead disc to crush it. This method of deriving the peak chamber pressure is limited in that it does not provide accurate or precise values for the peak chamber pressure, nor does it provide any data for the chamber pressure variation throughout a discharge of the firearm.
Other devices used include strain gauges such as the Oehler Model 43 which is a small strain gauge glued to the barrel over the firing chamber of a gun. Discharge of the gun causes the barrel around the firing chamber to expand momentarily and the strain gauge measures the expansion of the barrel which then allows a user to derive the peak pressure within the firing chamber from the measured expansion of the gun barrel. The strain measured on the barrel is proportional to the chamber pressure and can be used either as a relative pressure indication, or, an absolute pressure can be calculated using a pressure vessel formula.
Use of a strain gauge of this type requires a user accurately to measure both the inside and outside diameters of the chamber area of the gun at the gauge location. The use of the glue and the surface preparation of the gun surface which is required to attach the strain gauge thereto is likely to mar the bluing of the gun. For some users, this marring of the surface of the gun in addition to the requirements for obtaining accurate measurement of the firing chamber, is not acceptable. Furthermore, the requirement for having to attach the gauge to the barrel, means that it is difficult or even impossible to attach the strain gauge and any lead wires (going to a display meter) to some semi-automatic pistols.
The chamber pressure in a firearm is also measurable directly by use of specialised firearms which have been adapted or constructed solely for this purpose. Specialised firearms of this type generally have the firing chamber formed and arranged with a pressure meter attached or built directly thereinto in order to allow direct measurement of the chamber pressure. These specialised firearms can be expensive and are of limited value to a non-commercial interest such as an ammunition hobbyist.
It is also possible to modify standard firearms to allow direct measurement of the chamber pressure. Such a modification would comprise drilling a small hole into the firing chamber and attach a pressure measuring device over the hole. Discharging the weapon allows direct measurement of the chamber pressure. This destructive method is generally highly undesirable for obvious reasons.
More primitive and less precise or accurate methods of deriving the chamber pressure include affixing the firearm to a freely movable carriage to which a stylus is attached. Discharge of the firearm causes the carriage to recoil which draws the stylus across a high speed (approximately 10,000 r.p.m.) rotating cylinder which records the movement of the stylus thereacross. The acceleration of the carriage (plus firearm) can be calculated and therefore the force of imparted by the recoil of the carriage. Use of apparatus of this type requires that there be little or no vibrations near the apparatus during the test, as these would be detected by the stylus and would be prejudicial to the accuracy and precision of the results of the experiment.
It is an object of the present invention to minimise and/or obviate one or more of the foregoing problems of the prior art.
The present invention provides an apparatus suitable for use in measuring the peak chamber pressure of a given firearm upon discharge of said firearm using a given ammunition, which apparatus comprises:
a piezoelectric accelerometer for generating a recoil acceleration electrical output signal from recoil acceleration of the firearm upon discharge thereof, said accelerometer being provided with releasable mounting means formed and arranged for rigidly securing said accelerometer to said firearm in proximity to the chamber of the firearm, said accelerometer having signal output means;
a signal processing means;
first signal transmission means for transmitting said electrical output signal from said accelerometer signal output means to said signal processing means;
said signal processing means being formed and arranged to convert said recoil acceleration electrical output signal from the accelerometer to a second signal output which is representative of the peak chamber pressure, using a conversion relationship based on the mass of each of the firearm, and the projectile and the propellant components of the ammunition, and the firearm bore diameter, said signal processing means having signal output means for connection, in use of the device, to output signal display means.
Thus the apparatus of the present invention provides an effective means for readily determining the peak chamber pressure during discharge of a firearm without the need to resort to any destructive modifications to the firearm.
The firearm may be any regular handgun or rifle which is generally a commercial handgun or rifle which has not been specially constructed for the purpose of measurement of gun acceleration or chamber pressure.
The piezoelectric accelerometer mounting means is conveniently formed and arranged for releasable attachment to a telescopic sight mount prov
Border Barrels Limited
Hughes Robert B.
Hughes Law Firm PLLC
Raevis Robert
LandOfFree
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