When firing or when chambering a round?
I have had one slamfire in a AR15, witnessed one, I had three slamfires in M1 Garands, two out of battery, all with Federal Match primers.
AR Slamfire, with the new brass WSR, dropped a round in the chamber during the standing stage, hit the bolt release with my right hand, and the round went off taking a divot out of the dirt in front of the firing line. My hand was not on the trigger.
For the one I witnessed, the shooter was shooting standing and the same thing happened. He was using federal primers and I got to talk with him this year, and he had another standing stage with federals and that was the last he used federals in his AR15.
My Garand slamfires, first one sitting rapid fire, last round in the 8 round clip slamfired out of battery. Federal primers. Second one, standing stage, put a round in the SLED, pulled on the operating rod, the round slamfired in battery, federal match primer. Third one, firing from bench sighting a new match Garand from the clip, the rifle slamfired out of battery. Federal match primers. All of my 30-06 were from the same 5000 primer lot of federal match primers, that lot may have been particularly sensitive, or I was just unlucky. I am still using the trigger mechanisms of from the Garands that slamfired. They are mechanically correct and do not follow.
I have never bump fired a rifle. I have been shooting semiautos for decades now, I shoot with the rifle firmly in the shoulder. When shooting from position I have a tight sling.
I have collected lots of slamfire accounts, they happen in rifles. The most slamfiring rifle on the market is the Garand. M1a slamfires are rare, probably due to the lesser number. Foreign rifles with heavy firing pin have an unusually high number of slamfire accounts considering the low numbers of them out there.
You will never hear of a firing pin initated out of battery slamfire in a roller bolt, and I will bet you will never hear of a firing pin initated slamfire in battery either. The firing pin assembly does not move forward till the lugs are extended and the firing pin spring is very strong. It is so strong that I had to take it off to get the firing pin assembly to go forward for this picture.
AR15 slamfires were frequent enough that the NRA forbid loading on the shooting stool. And I know why. When you had a M1a you could load on the stool because slamfires did not happen on the stool due to rifle orientation and magazine friction. When shooting standing it was common practice, while at port arms, to press a round in the magazine then rest the rifle, butt down, bolt open on the stool, while your target was being scored. Sometimes you would see guys hit the bolt release on the stool as they brought the rifle back to port arms prior to cheeking the rifle. With the muzzle up, gravity was working against the bolt and the bolt was slowed by magazine friction. However, you cannot press a round in the magazine of an AR through the ejection port. Instead, I saw AR shooters put the muzzle of their rifle on the stool, drop a round through the port into the chamber, hit the bolt release, then bring the rifle up. Gravity was working with the bolt and increased the kinetic energy of the firing pin. Enough highpower shooters had slamfires through their stool, blowing metal fragments and dirt all over everyone around them, that this practice was forbidden.