Bullet Setback is effectively a non-issue because once a bullet has been setback far enough to cause pressure spikes high enough to be potentially dangerous, the whole round is so far out of spec that it won't feed from the magazine at all anymore,
This is pure nonsense. In some loadings, as little as 0.1" of setback will double the discharge pressure. I have some semi-automatics that will literally feed empty cases, the idea that a round that's a tenth of an inch too short won't feed in a gun like that is not credible.
...by that point it will most likely be easily detectable by the naked eye, ergo anyone with a lick of sense will discard it rather than attempting to chamber it repeatedly until it works then fire it.
I agree that it should be detectable, as long as people are aware of the possibility and are keeping an eye out for it. The idea that people would examine every round to see if it's shorter than it was when it was new without understanding setback seems unlikely. But yes, it is detectable by the time it's dangerous.
...you almost never see substantiated reports of Bullet Setback resulting in a KABOOM...
1. After the Kaboom, it can be difficult to find evidence of what caused it unless the round was examined before firing.
2. The people who are most likely to experience setback (LE who typically unload and reload/rechamber rounds frequently) have been educated about it as the result of documented incidents.
3. It's not likely to occur to people who shoot nearly exclusively at the range since rounds only get chambered once in most cases.
4. Not all loadings are especially sensitive to setback, so even when significant setback occurs, it's not guaranteed to cause a problem. If it's a lightly loaded round with a light bullet in a cartridge with a decent amount of capacity, then setback isn't going to cause a problem. It's only when the powder space gets very limited that reducing it further by setback can be dangerous.
Those two individuals conclusion was that while pressure may increase, it probably does not increase enough to cause a kaboom (at least in handgun cartridges).
Jim Ks first experiment was problematic because he used relatively light bullets for the caliber. Had he tried the same experiment with 147gr bullets, the results could have been much different. Furthermore, he did note pressure signs even though his experiment wasn't designed to maximize the effects of setback by choosing heavy for caliber bullets.
Tuohy's test is interesting, but since he gives us no other information about the cartridges he used for his tests nor the amount of setback in his "hammer tests", it's not really possible to know what the results mean. We know from ammunition manufacturer testing and from pressure calculations that some .40S&W loadings are very sensitive to setback. But the amounts of setback he initially tested were very small--maximum of 0.035"--unlikely to cause problems.
His hammer tests could provide useful results depending on how much the cartridges were setback (which he neglects to tell us) and on what the initial discharge pressures were. If they were lightly loaded cartridges with light for caliber bullets, then even a significant amount of setback would be unlikely to cause a problem, even in .40S&W.
Jim Ks second experiment was closer to what should have been done to really explore the situation. I don't think much needs to be said here because it seems like someone already responded to the important points on that thread.
...in my experience, they always mention handloads...
As far as I know, the issue first got serious attention in LE and involved commercial ammunition. It may be that more recent attention is focused on handloads, but that's not how it started.
...it being the leading cause or sole cause is dubious at best.
I'm not aware of any claims that it's the sole cause, the leading cause, or even that it's a common cause of catastrophic incidents. As far as I can tell, while setback is not that uncommon, it's not at all common for all the circumstances to come together in such a way as to result in setback causing an actual catastrophic incident.
It has the potential to cause such an incident, which is why it's important for people to know about it. But I agree, It's not the leading cause or the sole cause, or even a common cause of pistol blowups.
At the absolute most, bullet setback may be a contributing factor to KABOOMs when coupled with gross negligence, cartridges loaded beyond the pressure thresholds set by SAAMI or recommended in any reputable reloading manual, and/or design flaws present in the firearm such as an unsupported chamber lacking in adequate case head support.
This takes things too far. It can, in loadings that are sensitive to setback, result in impressively high discharge pressures from properly loaded, good quality, commercial ammunition. Pressures high enough to definitely cause a good quality firearm without defects to explode. Hirtenberger verified this some years ago, and anyone with Quickload can run the numbers for themselves to verify that what their testing showed agrees with the general principles of internal ballistics.
J.G. Terry said:
No more from me. ... That's all folks.
J.G. Terry said:
My point is that bullets do not collide with the fed ramp.
I provided a slow motion video of a 1911 feeding showing the slide hesitate when the nose of the round hit the feed ramp. It was quite obvious that the round hit the feed ramp and initially stopped, causing the slide to hesitate/slow before it forced the round up the feed ramp into the chamber.
I think it's pretty clear that the nose of a fed round will hit the feed ramp with significant force at some point in the feeding cycle--at least it's clear to anyone whose ever cleaned a pistol that's been fired with jacketed rounds. The copper streaks left on the feed ramp from the repeated hits from the noses of each fed round are not hard to see and can be difficult to remove.
Another interesting data point is the Beretta PX4. The feed ramp is polymer, but Beretta put a steel insert into the feed ramp to protect it. One wonders what they're protecting it from if there's no impact to it.
Finally, there have been a number of first person accounts on this thread of setback occurring from chambering ammunition. What's the rational explanation for how that happens if it's not that the bullet is being pushed back into the cartridge?
That hitting the feed ramp can be dismissed as a cause by actually looking at your handguns as the slide goes forward to pick up a round.
This is a puzzling statement is it's quite plain to anyone who has ever looked at most common autopistols that the nose of the round is aimed at the feed ramp and not directly at the chamber. Furthermore, hand-cycling an autopistol will show that in some designs, the round will impact pretty low on the feedramp where it takes significant force to "bump" it up into the chamber. That force works both ways--if it pushes the bullet forward, the impact also acts backwards against the bullet.
In short, there's a ridiculous amount of evidence that bullet setback does happen under the right circumstances.
There's more than adequate evidence demonstrating that it can result from repeated rechamberings.
There's absolutely no question that reducing COAL while holding other variables constant will increase discharge pressure.
There's more than an adequate amount of evidence that under the right circumstances, relatively minor amounts of setback (e.g. 0.1") can increase discharge pressure sufficient to cause a catastrophic incident. Hirtenberger did some testing that provided those results, but anyone with QuickLoad software can verify them.
Likely? No. But certainly possible. The key is, as Forte S+W points out, by the time it becomes severe enough that it could reasonably be expected to cause problems, it's quite easy to detect.
As long as people are aware of the potential problem and haven't been misled to believe it's a total non-issue. That's the main reason to let people know about the issue--because it's so easy to insure you never have a problem as long as you are educated on the topic.
Take one of these rounds and push down on it as hard as you can. See how much you can set it back. I think this set back stuff is a creature of the net.