How many accidental discharges occur from a long and heavy double action trigger pulls of 8+ pounds.
Here's a video of a female police officer discharging a Beretta 92 using the DA trigger pull. The hammer isn't back and her finger position indicates that the trigger is fully forward.
That would definitely be a long, heavy DA trigger with a pull of 8+ pounds. Stock pull is around 11lbs, and even with the lighter "D" spring it's still well over 8lbs. The video clearly showed that she did not intend to pull the trigger.
Given that
the most common cause of unintentional discharges (by far) is intentionally pulling the trigger, it should be pretty clear that the trigger type isn't a big factor in most unintended discharges. If the user wants to pull the trigger, they will simply disable any manual safeties that prevent it and if the trigger is long and heavy, they will just apply the force and pull required.
Looking at the linked poll shows pretty clearly that the weak link is usually the user and only rarely the gun.
You do know that ALL of the safety mechanisms in a Glock are disabled as soon as anything presses lightly on that finger dingus, right?
That is not correct.
Depressing the trigger safety disables ONLY the trigger safety. The firing pin safety and the ramp safety remain active (in safe) until the trigger movement actually begins--the trigger & trigger bar actually have to move for those safeties to be disabled. Trigger movement disables the firing pin safety and then the ramp safety, probably in that order.
It is true that actually pulling the trigger (moving the trigger and trigger bar back significantly) will disable all the safeties, but depressing only the trigger safety without moving the trigger itself disables only the trigger safety.
The internal safeties only prevent an accidental discharge if the gun is dropped.
They will prevent an accidental discharge from a drop, and it would even be accurate to say that's their main purpose, but it's not the only one.
They will also prevent an accidental discharge from some trigger snags because of the way the trigger/trigger safety is designed. It's not a sure thing for preventing trigger snags, but it actually works pretty well. I tested this using a Glock with a chambered dummy round and a magazine weighted with dummy rounds by throwing it into the air over a padded surface and catching it with a wooden dowel through the trigger guard. I was never able to get the mechanism to "fire" because after the initial contact with the trigger, the dowel tended to ride up the trigger to the portion where the safety could not be disabled before it could apply enough pressure to work the mechanism.
The internal safeties will also prevent a discharge in the event of parts breakage, defective parts, or inadvisable modifications. For example, if the "sear" breaks, or is modified so that engagement is too low and the striker is released, the firing pin safety will prevent the gun from firing.