I think you can assume that after you are rendered unconscious by your attacker that he will find the gun no matter where you concealed it.
Zimmerman had to assume that the guy who attacked him and was pounding his head into the concrete was not only going to take the gun from him after he was out, but to use it on him to eliminate any potential witness to the attack.
Let me ask you if you had a gun and a guy you didn't know and whom you suspected to be a burglar or other felon had you down on the ground and was bashing your head against the concrete, do you think you would not hesitate to pull out your gun from it's concealed location and use it?
Would you feel OK with the knowledge that if you were knocked out, that the attacker would not find the gun and use it on you because you had not "displayed" it?
Why add an unsubstantiated unconsciousness to the mix?
And once a reasonable certainty of serious bodily harm is established, any supposition of the perpetrators previous legal history is irrelevant.
Point is, Zimmerman’s history of respect for law enforcement (ancient history aside) and the training he received from the sheriffs dept. instilled in him a certain amount of procedural restraint. Otherwise that gun would have come out the second he ran into Martin again. But it didn’t.
My hypothesis is, Zimmerman, expecting a patrol car any second, backpedaled and fended off Martin’s advances as long as he could. Martin gained the upper hand and the gun was exposed as a result of the struggle. Martin went for the weapon, that’s when Zimmerman’s cries for help began. Some 40 seconds later the trigger is pulled.