I had a friend bring me three 9mm casings into work the other day. I thought I would take a look at them and report here since this may be interesting to some of you. The "story" is as follows. The names have been changed to protect the innocent (
).
A guy who my friend knows was shooting at a match a recent weekend. He was shooting a Sig P225 which was in apparently good condition. He was shooting some ammo which was reloaded by an unknown person, purchased about 15-20 years ago, and had been stored in a safe since then. During one string of fire, there was an extra large "bang" and firing was stopped. Upon inspection they found a case with a large blowout on one side. The gun was cleaned, inspected, etc and brought back the following weekend. With the same ammo, he was shooting again and heard another one. He realized, again, that the ammo casing had blown out the side and firing was stopped again. He discontinued the use of that ammo and was going to dispose of it. My friend was trying to get a sample so we could pull it down and at least weigh the amount of powder, although we might not have known what type of powder it was. The ammo was already gone at that point.
Evidence
Figure 1 is a photograph of three casings recovered from the ammo lot. All cases were marked "WCC 9mm LUGER".
Figure 1
The cases looked relatively clean and shiny on the outside. The main issue with them is the gaping hole on the side of 2 out of 3 down near the rim. On both cases, we can see a small crease of metal which indicated what part of the case was near the feed ramp. The most significant damage appears to be just off to the side (right side of the gun) from the deepest feed ramp crease. Extraction may have played a hand in this feature. Figures 2 & 3 show a single case rotated slightly between the images. Notice the blowout as well as the curved feed ramp indication. Figures 4 & 5 show similar images of the second case that experienced over-pressure to failure.
Figure 2
Figure 3
Figure 4
Figure 5
The casing which was not blown out and was simply picked up from the ground after being fired was found to have a slight bulge. The figure below (#6) shows this bulge, although you have to look closely.
Figure 6
It seemed relevant to point out that the primers had not been flattened. In fact, if you didn't know better you would say this is a really normal once fired 9mm casing by the evidence found on the case head. It looks perfectly normal.
Figure 7
There was a feature inside of the case near the floor with the flash hole around the outer edge which appeared to be a bit anomalous. Figure 8 below shows this feature on a blown out case, while Figure 9 below shows this feature on a brand new WWB unfired case. It appears this is simply a manufacturing artifact and is of no importance.
Figure 8
Figure 9
Finally, Figure 10 is a cross section image showing exactly how the case was blown out. I included a sectioned case which was brand new and unfired (WWB) for comparison. Notice that the blowout occurred through the thickest section of brass. Normally, overload fractures like these (overload meaning too much load and that the fracture happened all at once instead of fatiguing over time) find the path of least resistance. The fact that it went through the largest amount of material suggests the pressure was extremely high and that it was likely unsupported by the chamber in that location. In addition to this, the fracture surface of the material (visible back in Figure 3 appears woody in texture which is common on overload fractures in softer materials like low allow steels and brasses.)
I found no evidence of corrosion. Many types of corrosion can attack, weaken, and embrittle brass. The most common of these is dezincification which makes the brass weak and structurally unsound. I didn't see any evidence of this in close-up visual examination and in a metallographic cross section. One thing I haven't done, but would like to is scan this on a scanning electron microscope to see how much zinc is in the brass. I would have done this but the SEM is constantly busy these last few days. If it slows down I'll jump on it and put the results up here. I can't imagine any sort of "wrong material" issues as the places making these cases have very tight quality control.
Figure 10
Discussion
Looking at the evidence shown above, it looks as if the casing moved out of the chamber prior to blowing out. Since the gun appears to still be in good working order, and the barrel hood did not suffer any damage it doesn't seem possible that the case could have ruptured while still inside the chamber. The extreme pressure must have forced the case out of the chamber and the gun out of battery slightly to "unsupport" the case enough to allow for the blowout. The only other explanation I can think of is that the gun fired out of battery. Since the Sig P225 is a modern, reliable pistol that seems very unlikely. If anyone has other thoughts or discussion on this topic, please feel free to post below. This conclusion is just from us BSing back and forth on possibilities. The supposed root cause is too much powder in the case, but we can't verify this.
He's thrown out the ammo and the danger is gone, but I thought this would be a fun discussion topic. I'll report that the shooter suffered no real damage other than a little burn on his hand and the gun appears to be perfectly functional even after "kabooming" twice.
).A guy who my friend knows was shooting at a match a recent weekend. He was shooting a Sig P225 which was in apparently good condition. He was shooting some ammo which was reloaded by an unknown person, purchased about 15-20 years ago, and had been stored in a safe since then. During one string of fire, there was an extra large "bang" and firing was stopped. Upon inspection they found a case with a large blowout on one side. The gun was cleaned, inspected, etc and brought back the following weekend. With the same ammo, he was shooting again and heard another one. He realized, again, that the ammo casing had blown out the side and firing was stopped again. He discontinued the use of that ammo and was going to dispose of it. My friend was trying to get a sample so we could pull it down and at least weigh the amount of powder, although we might not have known what type of powder it was. The ammo was already gone at that point.
Evidence
Figure 1 is a photograph of three casings recovered from the ammo lot. All cases were marked "WCC 9mm LUGER".
Figure 1
The cases looked relatively clean and shiny on the outside. The main issue with them is the gaping hole on the side of 2 out of 3 down near the rim. On both cases, we can see a small crease of metal which indicated what part of the case was near the feed ramp. The most significant damage appears to be just off to the side (right side of the gun) from the deepest feed ramp crease. Extraction may have played a hand in this feature. Figures 2 & 3 show a single case rotated slightly between the images. Notice the blowout as well as the curved feed ramp indication. Figures 4 & 5 show similar images of the second case that experienced over-pressure to failure.
Figure 2
Figure 3
Figure 4
Figure 5
The casing which was not blown out and was simply picked up from the ground after being fired was found to have a slight bulge. The figure below (#6) shows this bulge, although you have to look closely.
Figure 6
It seemed relevant to point out that the primers had not been flattened. In fact, if you didn't know better you would say this is a really normal once fired 9mm casing by the evidence found on the case head. It looks perfectly normal.
Figure 7
There was a feature inside of the case near the floor with the flash hole around the outer edge which appeared to be a bit anomalous. Figure 8 below shows this feature on a blown out case, while Figure 9 below shows this feature on a brand new WWB unfired case. It appears this is simply a manufacturing artifact and is of no importance.
Figure 8
Figure 9
Finally, Figure 10 is a cross section image showing exactly how the case was blown out. I included a sectioned case which was brand new and unfired (WWB) for comparison. Notice that the blowout occurred through the thickest section of brass. Normally, overload fractures like these (overload meaning too much load and that the fracture happened all at once instead of fatiguing over time) find the path of least resistance. The fact that it went through the largest amount of material suggests the pressure was extremely high and that it was likely unsupported by the chamber in that location. In addition to this, the fracture surface of the material (visible back in Figure 3 appears woody in texture which is common on overload fractures in softer materials like low allow steels and brasses.)
I found no evidence of corrosion. Many types of corrosion can attack, weaken, and embrittle brass. The most common of these is dezincification which makes the brass weak and structurally unsound. I didn't see any evidence of this in close-up visual examination and in a metallographic cross section. One thing I haven't done, but would like to is scan this on a scanning electron microscope to see how much zinc is in the brass. I would have done this but the SEM is constantly busy these last few days. If it slows down I'll jump on it and put the results up here. I can't imagine any sort of "wrong material" issues as the places making these cases have very tight quality control.
Figure 10
Discussion
Looking at the evidence shown above, it looks as if the casing moved out of the chamber prior to blowing out. Since the gun appears to still be in good working order, and the barrel hood did not suffer any damage it doesn't seem possible that the case could have ruptured while still inside the chamber. The extreme pressure must have forced the case out of the chamber and the gun out of battery slightly to "unsupport" the case enough to allow for the blowout. The only other explanation I can think of is that the gun fired out of battery. Since the Sig P225 is a modern, reliable pistol that seems very unlikely. If anyone has other thoughts or discussion on this topic, please feel free to post below. This conclusion is just from us BSing back and forth on possibilities. The supposed root cause is too much powder in the case, but we can't verify this.
He's thrown out the ammo and the danger is gone, but I thought this would be a fun discussion topic. I'll report that the shooter suffered no real damage other than a little burn on his hand and the gun appears to be perfectly functional even after "kabooming" twice.
Nice report.
