Both the Danish and Norwegian versions utilize dual locking lugs (though asymetrical);
Just checked my Norwegian Krag (6.5x55mm mfg 1895 ser# 3xx), and it has one locking lug at the head of the bolt, and a second, much smaller lug on the body at the rear, which bears on the rear reciever ring.
Volley fire is a concept pre-dating machineguns. It was used two ways, defensively, as shown in the movie Zulu, the firing of squads by volley to repel an attacking charge, and by units (squad/platoon/company) against area targets at long range.
These targets were most often groups of enemy soldiers, cavalry, wagons, etc. Things in the open that could be seen. When you don't have machineguns, volley fire is your alternative for suppressive fire, at least until you can get artillery on target, assuming you can...
Never heard of rifle volley fire being used as indirect fire, but I suppose someone did it sometime, somewhere.
Many military concepts & tactics were retained long after improved technology rendered them obsolete. Volley fire is just one among many.
As to concerns about "wasting" ammunition, one can find this brought up (and often) in many militaries from the beginning of the repeating rifle era. Several nations retained single shot rifles much longer than necessary, simply due to the concerns about soldiers wasting ammunition, which, after all, cost money! And money is important, until you are actually fighting a war, and sadly, sometimes, even then.
The history of arms for the last century and a half or so is rife with examples of troops (of many nations, ours included) having less than the best, most effective weapons, because they were equipped in peacetime, and cost was a more significant factor than the lives of the troops.
Doctrines that seemed perfectly good during peacetime maneuvers often became instantly obsolete (and the weapons employed became less than the best possible) when combat showed the enemy wasn't operating by the same assumptions as our side.
WWII is a perfect example in hundreds, if not thousands of ways. With exceptions, the Axis pretty much stomped the Allies for a few years, before we caught up technically and tactically and finally won out.
back to the Krag...
a fine rifle for its day, and hugely superior to the rifle it replaced. Overtaken as a prime miliatry rifle by the Mauser design, the Krag still became a well loved and respected rifle, because of that. Large numbers of Krags were sold as surplus (at something like $1.50 from the DCM, and only a little more at retail) and the .30-40 round proved to be a big stick in the deer woods.
you could get a Krag and a LOT of ammo for what a Winchester or Marlin .30-30 cost, and the 180gr load for the Krag leaves the .30-30 well behind in lots of ways. One of the reasons so few "issue condition" Krags are around is because so many were sold to civilians, and "sporterized" by removing excess wood, and sometimes barrel as well.
The 220gr FMJ RN military load penetrates like you have to see to believe, and the 180 is no slouch in that either. Sedate by today's velocity standards, back in its day, it was fast, and powerful. The Krag killed dead everything that walks in North America (including the biggest record Grizzly) and did it as well if not better than anything else common at the time. Eclipsed eventually by the .30-06 in the sporting area as well, and never chambered in many rifles other than the Krag rifle (Win 95, and some single shots) the .30-40 Krag cartridge is still a favorite nostalgia round, and works as well today as it did way back then.
I've owned several Krags, and likely will get another .30-40 someday, but for now, my Krag rifle is a Norwegian 6.5mm, and my .30-40 is a Ruger No.3.