I use the sling (M1907 type) in most of my shooting, including hunting. In the Vintage sniper matches you can either use the sling, or sand bags, but not both.
I found I shoot my M1903A4 much better using the sling then I do using the sand bags.
The trick to using the sling, is using the sling properly. It should eliminate all use of muscles to hold the rifle. Upon recoil the proper sling position will always cause you to fall back to your natural point of (relaxed) aim.
Went on a bear hunt in Idaho this last spring. The guide saw my sling on my rifle ( an inline muzzle loader) and told me the sling wouldn't work for hunting saying I needed bi-pods. I don't have one and don't want one, I figured Id get buy.
So he puts me on my stand. Straight up and straight down. I had to dig an step to be able to set to observed the bait. Sling would work perfect, I noticed where I set a bi-pod would have to have 6 ft, legs to work.
The sling is lighter and faster the bi-pods, and doesn't get hung up in the brush.
Oh well, to each his own, I'll stick to my sling.