Hi jasche, I've been using two of these slings:
turner Slings Link
How to Use the Model of 1907 sling Link
They work well for what I want. I've hit groundhogs and bowling pins out to 150 yards with a 308 in the off-hand position with the 1907 model sling. Can't do that all the time though but I try. [img]/ubbthreads/images/graemlins/grin.gif[/img]
Usually I carry muzzle-down on my weak-side for a few reasons. One, I can quickly bring my rifle up for use, carrying a heavy-barreled rifle muzzle-up is a bit awkward for me and muzzle-down is a lower profile to non-hunters when you're walking the fields.
If you do go with this style of sling, turn the bottom hooks and strap so the hooks are pointing outwards. Otherwise they will dig into your shoulder.
The slings from Tactical Intervention Specialists look great and I may have to get one myself. The idea of a quick-cuff to wear on your arm is faster than getting into a 1907 sling.