Krag actions are smooth as glass because of the relatively tight tolerances between its moving parts and its glass hard carburized surfaces, in conjunction with its ingenious simple design in which the locking lug bears against a raceway, and the long extractor which rides in the split rear bridge. Both features act to keep the bolt from binding as it is moved in and out.
Many have decried its single locking lug in that it makes for a "weak" action. Truth of the matter is that it is fine for its intended purpose- 40,000 psi or so. (Remember this was the 1890's- low carbon carburized steel was the material of choice for a lot of gun makers. Stay at or under that and a Krag will last you another hundred years. Plus it has a huge safety lug also that absolutely will prevent the bolt blowing out in the absurdly unlikely event that the one lug shears off. Michael Petrov did an experiment in which he destruction tested a '98 Krag: Ever increasingly larger charges of Bullseye were employed starting at 5 grains, while firing the gun remotely, until it finally came unglued. The final charge was over 25 grains, making for ungodly pressures. The barrel and receiver ring were wrecked but the bolt stayed put- even though Michael had ground the locking lug off entirely, leaving the safety lug to do all the work.
Anybody who has ever had to load a rifle while suffering with cold numb fingers will speak lovingly of the Krag: just snap open the magazine and dump a handful of cartridges in and slam it shut. Charging clips that actually worked quite well were invented, but too late to assuage the naysayers who said it was slow to reload in combat. There's a guy over on the Krag collectors website who makes nice repros.
