Is it true? I read somewhere years ago that though the Krag has a single locking lug, the turned down bolt handle into the receiver rear, also acted as a locking lug.

remington:  As you mention, the U.S. Krag action has one locking-lug.  If that should fail, the rib on the bolt body and the bolt-handle root make contact with the receiver and serve as secondary or 'safety' lugs and help to keep the action from totally failing.  On U.S. receivers the rib and bolt handle normally do not make contact with the receiver.  On Norwegian and some custom U.S. Sporters, the bolt is fitted so that the rib on the bolt-body makes contact at its rear with the receiver.

The single locking lug is not really a detriment to the safety of the Krag...  unless you are loading hot rounds the lug should never fail.  If you're concerned, check out the following report on the Krag bolt:

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That is a great test and verification of the Krag action strength. PO Ackley documented strength of the Krag action in his article on strength of military rifle actions. The results with the Krag surprised him. It is clearly sufficiently strong for the ammo it was designed for.

Psteinmayer. Thanks very much for the access to the report on the strength of a Krag bolt. I would never had thought it is that strong!!!!

In all fairness, this was actually a test of the safety lug system. Note which failed first (the rear of the receiver) and how it failed (shattered). As one on another forum has pointed out, this is only a one rifle test. Yes - the Krags were sufficiently strong for their intended purpose. Their was still such variability in things like heat treat and forging processes to make the strength of the entire lot suspect when it comes to increasing pressure beyond the original 40,000 CUP design load. One other point - had the locking lug still been intact on this test rifle, it would have likely cracked long before the receiver safety lugs failed.

I would add that 30 gr of Bullseye would likely blow any rifle up :D

Good point... and duly noted!  I would never exceed even moderate loads in either of my Krags, under any circumstances.  They are just too precious to me.  I just think that the test is a good example of how safe the Krag action is, even if the lug does crack.  Of course, the Krag design does have it's shortcomings, but I love them nonetheless!  Besides, I can produce 1 to 2 inch groups at 200 yards with the open sights, and that is freakin' accurate in anyones book!!!