When is it best to get the shotgun?

[DaveMcDamage]

Hello all,

 

I'm currently on my first playthrough. Finding it tough simply because of how slow the main character moves. I cannot even tell that much of a difference between walking and running its so slow. Shame too as it would have made the game so much better with just a bit more pace. 

 

Anyway, I saw the shotgun but get locked in when I lift it so clearly its a puzzle. I then went upstairs and saw another shotgun behind a locked door, so I am assuming that for whatever reason I need that to do a switch perhaps. Anyway. I'm on the three dog head mission and using the collecatble guide text and vid and noticed a boss battle is coming up. Is it best to get the shotgun before going into that fight or should I save it for later? Ammo reasons and such.