NOTE:
The cartridges shown in the following article were all fired inside a closed test chamber while proof testing a new rifle action design with no risk of danger to the operator. The excessive pressures were achieved by grossly overloading the cartridges using the wrong powder for that cartridge type and these results show the dangerous pressures that are developed when cartridges are overloaded, or the wrong powder is used.
Do not ever attempt to test cartridges to this extent in a normal rifle in an exposed situation as severe injury or death may result or the rifle action may be damaged or destroyed.
Both calibres shown below were progressively loaded from a standard load as recommended by the powder manufacturer right up to the maximum pressure capacity of the recording equipment, 10,000Bar or 145,000psi to test the design and manufacturing quality of our new rifle actions. Click here to view a video on our pressure testing.
Unfired Norma case dimension at base, 0.546”. SAAMI lists this dimension as between 0.542” and 0.550”. There is often considerable variation in new case dimensions in all calibres due to the tolerances allowable under SAAMI rules.
Once fired 7mm SAUM cases from two different rifles. Fired case dimensions will vary depending on the chamber dimensions of the rifle the cartridge was fired in.
Note: Normal primer appearance indicating acceptable chamber pressures.
These series of photos show the expansion of the base of the cartridge when subjected to extreme pressure compared to a new, unfired case.
The very base section of a cartridge is not supported by the rifle chamber when fired and so can expand out to the diameter of the bolt face recess. The photo shows clearly where the chamber finished and the entire cartridge case head end has been expanded. The rim of the case was expanded tight into the bolt face recess.
Some case head deformation evident at this load and pressure in these two photos. Primer flattening, firing pin perforation of the primer, loose primer in the left hand case and gas leakage around primer in the right hand case. Some expansion of the unsupported section of the cartridge base as can be seen by the extruded ring just forward of the extraction groove taper
145,200PSI. (10,013 Bar)
The case was locked tight in the chamber and had to be driven out of the barrel with a long rod inserted up through the muzzle.
This case shows extensive expansion of the case head and extrusion of the brass into the bolt face recess and the space between the bolt face and the barrel face, start of chamber.
At this pressure case head separation was imminent.
The rest of the 7mm SAUM case appears undamaged as it was supported by the barrel chamber, which in turn is supported by the heavy steel ring shrunk onto the barrel to house the piezoelectric pressure transducer.
Action test assembly showing mounting block, our new 2 lug bench rest action and the transducer block shrunk onto the barrel. This is a prototype action, and some small changes have been made since this photo was taken. Chambered for the 6mm PPC testing shown below.
220 Russian Lapua Brass hydroformed out to 6mmPPC. Ejector pin removed from bolt.
Heavily flattened primer, firing pin perforation, case head expansion. No gas leakage past primer. Considerable case head expansion in the unsupported section of the case.
Severely flattened primer, Firing pin perforation. Case head expansion. No gas leakage past primer. Case head expanded tight into bolt face recess
Flattened primer, Firing pin perforation. Gas leakage past primer. Case head expanded tight into bolt face recess which is machined at 0.448”.
Flattened primer falls out easily, Firing pin perforation. Gas leakage past primer. Case head expanded tight into bolt face recess and has to be leveraged out from under the extractor. Damage to case rim caused when removing the case from the bolt face.
Note the extrusion of the brass into the space between the bolt face and the start of the barrel chamber.
At this pressure the case head was close to exploding in the unsupported section resulting in total case head separation.
During our rifle action testing procedures, we monitor chamber pressures produced by varying loads, firing pin lock times, firing pin performance, cartridge ignition consistency, bolt handle lift forces and smoothness of operation, case extraction and general action performance. All our prototype actions are put through this procedure and then returned to the workshop for NDT Ultrasonic crack testing, CMM measurement to check for any expansion of the action components, and close examination to look for damage to any components.
Our test chamber has been designed for action testing, rather than ammunition testing, but the Kistler piezoelectric transducers we use in testing are the same as used by NATO for ammunition testing and we follow the NATO test procedures.
The detail specs mostly looked at for the high speed data acquisition are both the sensor and the Data Acquisition Unit. (DAQ) The Kistler DAQ unit we own can collect data at 1 million samples per second. The Piezoelectric pressure sensor we use has a rise time of 2 µsec (a unit of time equal to one millionth (10⁻⁶) of a second.) and a natural frequency of 150kHz. These units combined can capture all the data we need to comprehensively test our rifle actions.
We also utilise an accelerometer to measure various ignition and lock times of each action so that any figures we publish can be verified by actual testing rather than theoretical calculations. An accelerometer is attached to the rear end of a specially manufactured firing pin and records first movement of the firing pin against primer strike time, first primer ignition time, first powder ignition time and finally peak pressure time. All of these actions can be seen in the graph produced by the recording equipment and are measured in milliseconds.
Actual Test Result showing the absolute maximum chamber pressure our 2 Lug action endured without damage. 199,286psi
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