My thoughts:
"3 times +3 Block versus detection as being anything other than a gun. So the DC to detect is 9." - You can't add three blocks together. That said, I don't think your end result is terribly far from unreasonable. The power creation rules indicate that you should get about 2 shifts of effect from each point of power, and that the first point can have a bit of extra benefit. So requiring an Epic (+7) roll to detect the magical properties of the weapon (3 for the first refresh, +2 for each of the others) seems right. This would be an 'always on' ability, not a three-use ability.
"You are the target(Guns): When the target defends and tags its aspects they are only worth +1. If a reroll is used, you may lock down one of the dice of the 4df leaving the reroll to involve only the other 3 diced (just like the stunt Unshakeable)." I understand where you were going here, but I don't feel entirely comfortable with reducing the effectiveness of another character's personal aspects. I'm more comfortable with putting modifications like this on people's use of external aspects (like scene aspects or maneuvers, or use of other people's aspects), like you did in one of the other variants. Alternatively
"Forced release(Guns): If the enemy defends against a Ricochet, Max can forgo his next action in order to remove the aspect of Human Shield, etc. at +1." I'm not entirely sure how to interpret this.
"Inhuman Strength, applied to the gun: +3 when breaking to objects + 2 extra stress general." I'd change this to "+3 when breaking to objects +2 extra stress general" -- that is, remove the reference to Inhuman Strength, because holding the gun shouldn't give bonuses to grappling, for example.
"Claw, poison, in the form of Claw, fire." As written, this would count as a melee attack. I think you'd need to base this on Breath Weapon, instead. Given that the two are identical except that the ranged one costs an extra point, it seems reasonable to allow you to apply 'Venemous' to the Breath Weapon attack. Though this would cost 4 refresh, which is too much.