Hi, guys,
From time to time, someone reports that a gun, usually an auto pistol, "blew up" due to bullet setback. This is supposedly a condition where cartridges in a magazine have the bullets pushed back in the case either due to impacting the feed ramp if one round is chambered repeatedly, or due to recoil causing bullets to contact the front of the magazine and be forced deeper into the case. No matter what the cause, a bullet seated deeper than normal will supposedly cause extremely high pressure, enough to blow the gun up or cause the case to fail and cause serious damage to the gun.
At one time, I tested rifle loads by deep seating bullets and, while I found signs of a moderate pressure increase, I never found any pressure rise sufficient to cause damage to a gun. But I thought the case with handguns might be different.
So when I recently heard again of bullet setback causing a pistol to blow up, I decided another test was in order. As is common in these reports, the person providing the information did not know when or where the event occurred, did not witness the event, was not the shooter or owner of the gun, had not seen the gun, and did not know any details. No analysis of the gun or ammunition had been done by any knowledgeable person.
So, I set out to create "bullet setback". Since many of the pistols supposedly involved were 9mm Parabellum, I chose that caliber for my tests. Not wanting to take a chance with a pistol, I used a Ruger Blackhawk with a 9mm conversion cylinder. Even though the revolver fully supported the case so it could not blow out, I felt pretty sure that I would see signs of any pressure so extreme that it would cause a cartridge case to fail or a barrel to burst.
I chose three types of factory ammunition, all FMJ ball. They were Magtech, a Chinese brand; Winchester; and a Finnish submachine gun load that is very "hot".
The cartridge overall length of all was the same, 1.164" +/- .002". The Chinese bullet was 124 grain, the others 115 grain.
I did not use a bullet seater to push in the bullets since I did not want to crimp them. I used a vise, thus simply pushing the bullets in, as supposedly happens in pistols.
In each cartridge, I found bullet movement difficult, as the bullets were sealed in the cases. In my opinion, that alone would have prevented bullet setback with factory ammunition, but it made no difference to the testing since the seal was broken when the bullet was pushed in.
For each ammunition type, bullets were seated to a cartridge overall length of (a) 1.120", (b) 1.050", (c) 1.020". A fourth was not seated to a specific COL but the bullet was forced into the case as far as it would go, compressing the powder charge. I prepared two rounds of each depth of each type, including two factory rounds of each type as controls, for a total of 30 rounds.
The result? First, the old Ruger is intact, and so am I. All the "hot" Finnish rounds were hard to extract, but the primers showed no significant pressure increase. Only two cases showed any significant flattening of the primer, a Magtech round with the bullet seated to 1.050" COL, and a Winchester case with the bullet seated down on the powder. There were no other signs of high pressure. None of the other brands showed any extraction problems. There was no noticeable difference in recoil or noise (I was using ear protection, of course), even with the Finnish ammuntion.
So my conclusion is the same as before. Bullet setback may cause some rise in pressure, but not enough to "blow up" a gun. I am not saying the stories are untrue, only that some other factor would appear to be involved. I also suspect that the situation is a lot less common than believed, probably because once a story gets started, it will be repeated and elaborated on until it seems to be happening all the time. Bullet setback would be an easy explanation for any problem that no one is prepared to research. It could also be an excuse for a more likely problem, like an overcharge in handloads.
I recognize that my experiment was limited and used factory ammo only. I could not possibly test all conceivable handloads, or all calibers. But some reports did state that the ammunition was factory FMJ and I think I covered that reasonably well.
Jim
From time to time, someone reports that a gun, usually an auto pistol, "blew up" due to bullet setback. This is supposedly a condition where cartridges in a magazine have the bullets pushed back in the case either due to impacting the feed ramp if one round is chambered repeatedly, or due to recoil causing bullets to contact the front of the magazine and be forced deeper into the case. No matter what the cause, a bullet seated deeper than normal will supposedly cause extremely high pressure, enough to blow the gun up or cause the case to fail and cause serious damage to the gun.
At one time, I tested rifle loads by deep seating bullets and, while I found signs of a moderate pressure increase, I never found any pressure rise sufficient to cause damage to a gun. But I thought the case with handguns might be different.
So when I recently heard again of bullet setback causing a pistol to blow up, I decided another test was in order. As is common in these reports, the person providing the information did not know when or where the event occurred, did not witness the event, was not the shooter or owner of the gun, had not seen the gun, and did not know any details. No analysis of the gun or ammunition had been done by any knowledgeable person.
So, I set out to create "bullet setback". Since many of the pistols supposedly involved were 9mm Parabellum, I chose that caliber for my tests. Not wanting to take a chance with a pistol, I used a Ruger Blackhawk with a 9mm conversion cylinder. Even though the revolver fully supported the case so it could not blow out, I felt pretty sure that I would see signs of any pressure so extreme that it would cause a cartridge case to fail or a barrel to burst.
I chose three types of factory ammunition, all FMJ ball. They were Magtech, a Chinese brand; Winchester; and a Finnish submachine gun load that is very "hot".
The cartridge overall length of all was the same, 1.164" +/- .002". The Chinese bullet was 124 grain, the others 115 grain.
I did not use a bullet seater to push in the bullets since I did not want to crimp them. I used a vise, thus simply pushing the bullets in, as supposedly happens in pistols.
In each cartridge, I found bullet movement difficult, as the bullets were sealed in the cases. In my opinion, that alone would have prevented bullet setback with factory ammunition, but it made no difference to the testing since the seal was broken when the bullet was pushed in.
For each ammunition type, bullets were seated to a cartridge overall length of (a) 1.120", (b) 1.050", (c) 1.020". A fourth was not seated to a specific COL but the bullet was forced into the case as far as it would go, compressing the powder charge. I prepared two rounds of each depth of each type, including two factory rounds of each type as controls, for a total of 30 rounds.
The result? First, the old Ruger is intact, and so am I. All the "hot" Finnish rounds were hard to extract, but the primers showed no significant pressure increase. Only two cases showed any significant flattening of the primer, a Magtech round with the bullet seated to 1.050" COL, and a Winchester case with the bullet seated down on the powder. There were no other signs of high pressure. None of the other brands showed any extraction problems. There was no noticeable difference in recoil or noise (I was using ear protection, of course), even with the Finnish ammuntion.
So my conclusion is the same as before. Bullet setback may cause some rise in pressure, but not enough to "blow up" a gun. I am not saying the stories are untrue, only that some other factor would appear to be involved. I also suspect that the situation is a lot less common than believed, probably because once a story gets started, it will be repeated and elaborated on until it seems to be happening all the time. Bullet setback would be an easy explanation for any problem that no one is prepared to research. It could also be an excuse for a more likely problem, like an overcharge in handloads.
I recognize that my experiment was limited and used factory ammo only. I could not possibly test all conceivable handloads, or all calibers. But some reports did state that the ammunition was factory FMJ and I think I covered that reasonably well.
Jim
