First off, are we just talking handgun cartridges? Because rifle reloading is a whole nutter matter.

In the case of a handgun, too long is not that big of an issue. Usually, and especially in a revolver, you aren't going to "run into something" that will cause pressures to increase. If things get that long in say, a 38spl, most likely, you are not going to get the cylinder closed. In an auto, I suppose that you can run into similar trouble BUT, again, the action shouldn't close if too far out of battery, and still, no kaboom.

The problem is in handgun cartridges where the OAL is shortened and there is more bullet in the case than the "recipe" expected. Now, if you are doing your reloading correctly, starting low and working up will save you precious body parts and maybe even a loving bystander or two. No harm, no foul. The problem comes into play when you are using a super fast handgun powder and reduce the amount of "free space" in a case with the same amount of projectile weight. Depending on the powder, you can have a real bad episode on your hands.

Case in point: 40S&W, 180gr bullet, Clays powder, bullet setback of .060" or something more with a full charge. What are you going to have when you pull that trigger? Right, you don't know and in the wrong handgun, you could have a catastrophe.

There are other factors that play a part too, bearing surface being one of them. BUT, I firmly believe, you don't have to agree with this, that seating depth is the most critical thing to causing a dangerous pressure spike that a reloader/handloader can overlook or change.

Listen, Elmer Keith's whole premise on the designs of his bullets rests on this one point: More bullet outside the case reduces pressures inside the case. Fill that extra space with powder and then the pressure can be raised to new and exciting levels! (Just an attempt at some dry humor.)

The reality is, more empty space in a straight walled pistol cartridge, same amount of powder and bullet weight will reduce the pressure in the case. Seat the bullet deeper, pressures increase.

Just my