An ESi investigation combines metallurgical, mechanical and chemical analysis to determine the cause of a rifle accident. ESi ultimately contributes the powder analysis to the National Center for Forensic Science Smokeless Powders Database.
In September 2015, a Winchester Model 70 rifle was taken to a gun shop to have a new scope mounted and sighted in.
The gun had been originally manufactured in 1949 with a .300 Holland & Holland (H&H) Magnum chamber. The rifle had been modified into a .300 Weatherby Magnum (WBM) chamber prior to its sale to the current owner.
Upon completion of the installation of the scope, the gunsmith fired the rifle to check the scope. A new box of commercially reloaded ammunition was used for the testing. The first round fired successfully.
When the second round was fired, an explosion broke the rifle apart with a catastrophic failure of the rifle’s receiver, injuring the gunsmith.
ESi was retained to investigate the cause of the explosion.
The rifle was evaluated to determine if there was any preexisting damage prior to the incident. The methods used were nondestructive and non-altering, and included visual, photographic, and optical microscopic analyses in addition to scanning electron microscopic (SEM) evaluations.
The cartridge contents were also chemically characterized and evaluated to identify the type, brand and size of the powder. Documentation of the powders included shape, dimensions, luster and perforations. The powders were ultrasonically solvent extracted and analyzed using gas chromatography-mass spectrometry.
The cartridges in the ammunition box were examined to determine their consistency and adherence to the maximum reloading ranges. A lab exam measured the overall length, headspace, pull force, and weights of the powders and components. ESi reviewed the SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) standards, chambering and cartridge drawings for the .300 H&H and .300 WBM. NECO QuickLOAD© software calculations were run for Alliant Powders Reloader® 25 and Reloader® 15 along with the powder recipes listed in the bullet manufacturer’s guide.
Metallurgical evaluations determined that the force that caused the damage originated from the cartridge during firing and that there were no preexisting fractures, fatigue striations, or damage to the rifle prior to the incident. This force was oriented backwards against the bolt face and was sufficient to force the bolt backwards and upwards against the receiver, causing the receiver to deform and fracture. All the receiver fracture surfaces were ductile in nature, demonstrating they were all caused by the single overload event from the discharge of the cartridge.
The mechanical investigation showed the cartridge’s powder weight within a range from 85.0 to 85.4 grains with an average of 85.2 grains. This would be within commercial tolerance and should not result in unsafe loadings with the proper powder.
During the chemical examination, one cartridge was found to be loaded with a different powder based on the size of the grains and chemical analysis of the powder. The powder examined for all but one cartridge was Alliant Powders Reloader 25. The powder examined in the one cartridge was Alliant Reloader 15.
It was determined that the cartridge used during the unsuccessful firing contained the Reloader 15 powder. Using the incorrect powder within the ammunition was the causation of the excessive pressure and ultimate explosion.
As an additional outcome from the extensive work on chemical characterization and identification of powders using methods outlined in ASTM E2998-16, ESi was able to contribute a comparison of the results to the National Center for Forensic Science (NCFS) to be added to their Smokeless Powders Database.
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