Re: AR 15 Malfunction.
Free flying bolt struck a stalled round. Neither condition was normal. The situation looks like a classic instance of a slam fire.
In the future; remove mag, lock back bolt, and try to extract the stalled round by prying against the extraction groove..
If this is not possible, gently guide the bolt forward to meet the cartridge base using the t-handle, then open the upper and remove the BCG. Gently ease the cartridge out of the chamber using a cleaning rod. If it will not respond, try to pry it out by the extraction groove.
The problem occurred because the bolt was allowed to fly free at a stalled round. This defeats the design safety features which expect the bolt's velocity to be curtailed by the friction/drag caused by feeding a round from the magazine. IMHO, most slamfires are caused by improper handling. A bolt should never be allowed to fly free toward a chambered or partly chambered round.
This is not likely a heat issue.
Raised primers are more likely to cause a misfire than a slamfire.
Until a primer is fully seated the anvil legs have not properly preloaded the priming pellet, sensitizing the primer. Most usually, the first firing pin strike completes the primer seating process, but also absorbs enough energy from the firing pin that it is unable to fully initiate ignition. Generally, the primer will ignite on a subsequent second strike. This 'second strike ignition' syndrome generally confirms the presence of an incompletely seated primer.
Greg