Re: How common are "slamfires"?
It seems that it has something to do with the free-float firing pins in military type weapons. When the bolt slams forward with force, the inertia of the firing pin will cause it to strike the primer. If the primer is not hard enough or seated properly, the cartridge will fire. If it happens when the bolt is not fully locked, it can destroy the firearm and the shooter as well. SCARY!
Laws that forbid the carrying of arms... disarm only those who are neither inclined nor determined to commit crimes... Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than to prevent homicides, for an unarmed man may be attacked with greater confidence than an armed man. Jefferson's "Commonplace Book," 1774_1776, quoting from On Crimes and Punishment, by criminologist Cesare Beccaria, 1764