Back in the days of the fighting bolt action rifle, clever small arms designers came up with a number of minor but ingenious features to make the soldier’s life a little less hard when trying to cycle their rifle’s action by hand as they faced down the enemy. Many of these special features have since made their way into many of the world’s modern hunting rifles, but they were pioneered by designers coming up with new and better weapons of war.
One of these detail features that got a decent amount of press and attention once upon a time is called primary extraction. The idea here was that a rifle would have some kind of special camming surface in the receiver which would act against surfaces on the bolt to provide a mechanical advantage in the initial part of extraction. If the rifle had a stiff case, this extra leverage would help the soldier get the case unstuck from the chamber so that he could continue fighting.
To better illustrate how this works, TFB’s own Mike B on his channel Bloke on the Range set up a few rifles with deliberately bunged-up cases to show his viewers how a little extra leverage goes a long way: