back into civilization.
This isn't necessary, we know that's where they're most likely being released.
Participants have impossible knowledge of how the issued firearms work.
What do you mean by this? How is the knowledge impossible?
SCP-2571-A giving victims a cold stare
I'd say "assuming a hostile expression while maintaining eye contact."
Upon the death of an SCP-2571-A instance, subject will begin a period of rapid decomposition until reaching the approximate state of decay that a body deceased for 40 years would exhibit.
How long does this take, exactly?
and has never missed a shot.
That we know of. I'd change it to "has never been observed missing a shot."
Admittedly, I don't know much about the Alamo, but this seems more than vaguely disjointed and doesn't have a lot to tie it together. Why is Davy Crocker anomaly man having these effects on his victims? Is there something to do with his history? There should be more to this than just anomalously committed re-enacters who suffer a random yet horrible fate occasionally.
But that's all it seems to be atm.