For period correctness, the 1887 style sling in 64 1/2 inch length, is the type most seen in photographs. It is basically a carry strap and not really designed as a shooting sling.

Around 1903, it was being improvised for position shooting, by threading it through the barrel-band swivel and attaching it to the front 'Stacking' swivel.

Many of the reproduction model 1887 slings are being made 70 to 72 inches long. They may work on a 'trapdoor' Springfield, but, are too long for use on a Krag. They are too long to make them taught on a Krag.

I have gotten a couple of 64 inch repros on ebay. It is kind of luck of the draw. They aren't too bad once they are made more pliable with leather dressing and stop smelling bad.

Strangely, as a shooting aid on 'trapdoors' and Krags, the model 1887 sling was used with the shooter's foot in the old "back position".

The Krag 'web slings' were pretty much an experiment, around 1902, and proved unsatisfactory. I don't think I've seen a picture of one in use.

The 1907 Sling was developed for the 1903 Springfield, both for carry and as an aid for position shooting. It is used by most of the guys who are shooting the Krag in competition.

There are probably decent replicas of the 1907 sling on ebay.

Original slings of all types have gotten expensive and often have age cracks.

New Model 1907 Slings made by Turner Sling are highly regarded and probably entail a wait.

FWIW - I don't leave slings on rifles. It is not good for the leather or for the metal.