Rifle slings have saved the lives of more critters than PETA. Used incorrectly, a sling (or more properly, a carrying strap) can place your rifle out of reach for more than enough time for an animal to bolt and die of old age.
Sling misuse can have even more serious consequences. Many years ago, I was on the trail of a highly irritated lion in the Kalahari Desert of Botswana, .375 slung over my shoulder. Ian Manning, the professional hunter whose job it was to keep me from becoming lion poop, said, “David, do you really think the bloody lion is going to wait for you to unsling your bloody rifle before he bites you in your bloody arse?” I had offered to fight Manning the day before when he said my rifle looked like it belonged to a French nobleman, but there was no doubt he was making sense about the sling.
The only situations in which your rifle should be slung is when you have no intention of shooting anything or when you have to use both hands for something. (You should not sling a rifle while getting into a tree stand; instead, get in the stand first, then pull the unloaded gun up with a rope.) The rest of the time, put the sling in your pocket and be ready to shoot.
There is a way to sling a rifle that allows you to bring it into action quickly and use the sling as a shooting support at the same time. In the past when I have recommended this technique, I set all the Safety Nazis in a frenzy. To them I say: One hand is always on the rifle and has it under constant control. It’s not as though the gun is swinging freely, doing whatever it pleases. I learned how to do this in 1958 from a gun writer named Francis E. Sell, who had probably used it for 50 years at that point. I have been using it for 46 years. Sell did not shoot himself in all that time, and neither have I, so spare me.
It works like this: Assuming you have a smooth rifle sling and not one of the grabby kind that won’t slip off your shoulder, and assuming you’re right-handed, you sling the rifle over your left shoulder, muzzle down, trigger guard forward. Your left hand should be on the fore-end to control the movement of the gun.
When it comes time to shoot, you simply haul the rifle up and put the butt in your right shoulder. The sling remains looped around the upper part of your left arm as a brace. This can be done in one motion with a minimum of movement and is very fast. And, as the signs correctly say, speed kills.