There are two issues I noticed when it comes to using shooting slings for field use: (1) Most shooting slings are slow to get into; (2) there aren't any really good options for a shooting sling that works like a 2-point tactical carry sling, letting you hang the rifle out front in low ready, which I consider to be better than traditional over-the-shoulder carry for a lot of reasons.
So I designed my own quick-adjust 2-point tactical carry sling that also works as a marksman's sling. I used 1.25" nylon webbing and all parkerized steel hardware. The front strap of the sling is an arm loop that you pre-set to where it gives you good support in all positions. Once you set it, you leave it alone. The rear strap is where you adjust the overall length of the sling for carry, with the quick-adjust keeper that goes close to the stock. I designed it so that you set a "go-to" length on the rear strap for your normal "moving and shooting" setting, then you can cinch the sling up tighter for retention while carrying, and when you need to shoot you can quickly pop it out to the "go-to" setting and take care of business. The buckle that sets your "go-to" setting also keeps the trailing end of the adjusting strap from flapping all over the place when you have the sling cinched up. So as a carry sling, it does anything any other tactical 2-point does: front side low ready, over-the-back, and even backpack-style for splitting the rifle's weight on both shoulders for long hikes. It works great with all your close quarters moving-and-shooting techniques, or for taking snap shots in a hunting situation. Then if you need some extra support for a smaller or longer-ranged target and you have a few seconds to sling up, you just pop your arm through the forward loop and wrap your wrist. You can get slung up with this thing in under 3 seconds, and can get back out at least as fast. It's about as fast as a Ching to get in and out of... but of course a Ching is only designed for shoulder carry. And plus with mine you don't have to drill for that annoying middle swivel. I call it the "DR Sling" because 1) those are my initials, and 2) it is dual role: carry strap and marksmanship aid. It works best with side swivels if you're going to use it for tactical carry, but on bottom swivels you can adjust it a little shorter and it works fine for traditional over-the-shoulder or African-style carry. Anyway, it works great for me. I have given some thought to selling them. Here is a DR sling on my AK, with side mounts:
I consider the shooting sling a very effective "tool for my toolbox." It is not ideal for every situation, but there is no doubt that in skilled hands it is a very effective marksmanship aid. For anything but a dedicated long range precision rifle, I prefer a sling to a bipod. A sling is much lighter, less bulky, and less obtrusive, and it is more versatile. A bipod requires a relatively flat surface that is at the correct height under your position... not something you can always count on in the field. Same thing with a solid rest... you can't always find something suitable in the field, and it limits the positions you can use. By contrast, you can use a sling in just about any position... standing, kneeling, seated, prone -- and in prone, I am just about as stable in a good tight sling as I am off a bipod. One of the most common positions I use in the field is sling-supported kneeling. Kneeling is really quick to get into, offers a lot of stability over standing, keeps your hindquarters off the ground, and is usually high enough not to be obscured by foliage. The sling REALLY tightens it up. Also, you can use a sling in conjunction with solid support... a slung-up standing position while using a tree, building corner, or doorframe as support is rock solid.