On the science behind case cracking in the article below. based on problems faced by the British Army in 19thC India. Though the brass manufacturing has come a long way since, this gives a good chemical explanation behind weakening of the brass. Coupled with the IOF's apparent disregard for uniform and proper loads, it would result in cracking. That brasso explanation is pretty decent tho.
Article taken from -
http://openlearn.open.ac.uk/mod/resourc ... FIG001_022
2.6.2 Cracking of copper alloys
Stainless steel is not the only metal to fall victim to SCC (stress corrosion cracking). One of the first discoveries of SCC occurred in India in the early part of the nineteenth century, when that country was still part of the British Empire. There was a large standing army that was always in need of live ammunition. The brass cartridge cases would occasionally split, and often at the worst possible time (when being fired), frequently causing injury to the marksman.
So what caused such failures? The two factors needed for stress corrosion cracks are, first, a tensile stress in the outer layers of the brass and, second, an active chemical that will attack brass or copper. The stress could be caused by the manufacturing forces used to shape the cartridges, since the cases were made from cold-deformed brass (70% copper, 30% zinc). The process involved successive stages of deformation of flat discs punched out from 3.25 mm thick sheet (Figure 22). After each stage, the product was annealed in order to recrystallise the metal, and pickled with sulphuric acid to remove oxide at the surface. The annealing process was intended to relieve residual stresses set up in the cases, but the process was not always successful in completely removing these stresses.
[img2=
http://openlearn.open.ac.uk/file.php/32 ... 1_022i.jpg]Figure 22: Process used to make cartridges[/img2]
After some detective work, an association was seen between the rate of cracking and the season of the year. Cracking tended to occur during the monsoon season when humidity and temperatures were high, rather than during the cooler months. Yet although the rate of most chemical reactions increases with temperature, controlled experiments showed that this could not have been the only cause of the problem. Then the Woolwich Arsenal undertook a series of trials with many different chemicals. They exposed bent strips of brass to the chemicals and observed the metal surfaces at the most highly stressed zones. They found that ammonia gas and water vapour were, in combination, the two most potent agents needed to initiate brittle cracks. Bearing in mind the experience of stainless steel in chlorine-doped water, it is interesting that failure times for many samples dipped into ammonia solutions were longer than for exposure to ammonia gas and water vapour.
The mystery was therefore solved, because it was realised that ammonia is produced by manure and dung, so would have been present in the stables of the army horses, for example. If ammunition had been stored near the stables, it is most likely that trace amounts of ammonia in humid air could have cracked the brass cases extremely quickly. Hairline or microscopic cracks would have been formed, and then grown to a critical size by the time the ammunition was needed.
So why does cracking or highly localised attack occur in such a case, rather than general corrosion? The active agents attack at stress raisers, at the upper edge where the case makes contact with the bullet [img2=
http://openlearn.open.ac.uk/file.php/32 ... 1_023i.jpg](Figure 23)[/img2]. The formation of a galvanic cell is unlikely, because a thin film of water on the surface is insufficient to provide the electrolyte. However, the final stage of manufacture, when the bullet is put in the explosive-filled case, will put the lip under a radial or hoop stress. The edge is unlikely to be totally level, and small degrees of roughness there will be attacked by the ammonia. Once a crack has formed, it will grow under the influence of the hoop stress, with the corrosive solution seeping away to leave a fresh crack tip ready for further attack.
“To be both a speaker of words and a doer of deeds”- The Iliad.
all my revolver ammo to make it shiny
like in the gun magazines.
