I watched the Steponallofus interview last night.
Baldwin explained exactly what he did.
He pulled back the hammer and before it locked he released it and it slammed into the round with enough momentum/force to ignite the primer. No trigger required. Pretty basic.
I’m thinking they were doing some fun shooting with live rounds earlier in the day and forgot to remove the live rounds. Just my take.
“He pulled back the hammer and before it locked he released it and it slammed into the round with enough momentum/force to ignite the primer.”
That is, for all practical purposes, pulling the trigger.