[Covax]

Step back enough that your muzzle is on the corner (pistol, carbine, whatever) then swing your body around in an arc with the comer as the center point. Like circle strafing. That way you have your muzzle out, and more importantly UP, roughly the same time your meat is exposed.

You can practice this with a mirror.

It's not the most efficient way to round a corner but when violence of action is needed that's gonna be your best option.