It's just more safe to pull a gun up horizontally than vertical. I guess if you want to worry with tiring a slipknot around the stock thats your call, but unless you plug the barrel in some way, this isn't the optimum option.
What are you talking about? A weapon pointing down seems safer to me. That's 3 overhand knots(very complicated). If you throw your weapon out of your stand, you might get something in the barrel.
