This isn't that much of a deal if its in the game or not to me. But I was just wondering if you can walk with your gun holstered or not?

I don't know if you can "holster" your gun. But if need be you can remove your 2ndary weapon and switch to the empty selection which will cause you character to stand with hands on hips.

As far as "Walking" + Shooting: Totally. I believe that walking has the same effect as crouching while moving around. It may minimize your noise and the likelihood of being spotted.

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