After monkeying around with bullet setback for several years my conclusion is that there is only one brand of commercial 45 Auto ammunition that doesn't suffer setback upon chambering in a 1911 and it tops the list below:
And the reason the PMC I tested suffered no setback is because its bullets are sealed to the case with some sort of waterproofing agent - just like most military ammunition.
Based on all the tests done I'd have to conclude that setback to varying degrees is normal and setback varies a lot with the number of rounds in the magazine:
• The first couple of rounds fed from a full magazine will get set back the most because these rounds hit down low on the frame feed ramp.
• The last few rounds fed from the magazine get set back the least because they either hit the frame feed ramp up toward its top or may not hit the feed ramp at all.
Furthermore, there's nothing at all that can be done to prevent the fist few rounds from a full magazine from hitting the feed ramp down low. That's because it's all a result of the amount of nose support the top round gets from the rounds below, as shown below:
And the only - repeat - ONLY way to avoid having a gap under the nose of the top round of a full 1911 magazine (and avoid any chance of bullet setback) is to have a magazine in which all the rounds are directly above the one below. And that would involve changing the 1911 magazine well angle from 17½° to 0° - or straight up and down.
While it's certainly true that bullet setback will cause an increase in chamber pressure, that increase in chamber pressure doesn't seem to be a problem (unless you're in the 1911 Benchrest crowd). I've also concluded that bullet setback becomes an issue only when it cause a 1911 to jam. And it can. Following standard loading procedures and using factory components I've even loaded up some test rounds that are just about guaranteed to make any 1911 jam with the bullet nose planted firmly on the feed ramp - all due to too much bullet setback.
When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
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