When Sweden and Norway adopted the 6.5x55 cartridge, 'way back in the very earliest days of smokeless powder, they did so with a very long, round-nosed bullet of about 160 grains weight. This is what all Swedish and Norwegian military ammo was loaded with for the first half-century of the round's service life.
Needless to say, although it appears that it needs to be said, rifles of the period were throated for the existing ammunition.... which meant a long throat.
The pointed 139-grain boat-tailed bullet made its appearance in 1941, at which time Norway was under German occupation (after Swedish help in getting the Germans there), Denmark was under German occupation.... and only 4 miles way across the Sound. Sweden was supposedly neutral, as was Norway, but the country was manufacturing lots of goodies for Uncle Adolf (including ball-bearings and specialty steels). Most Swedes did not like the situation, the country was getting very close to a war footing and slowly started to behave like a true Neutral rather than as a frightened Nazi cheering-section. Stockholm ("Fish Beach") was a popular getaway for uppercrust Nazis and the Brits had their spies and diplomats there in droves. Sweden provided a good number of Camp Inspectors to the International Commission of the Red Cross and they did excellent work for EVERYONE. Gradually, Swedish gunners lost the knack of hitting Blenheims and Hurricanes and learned how to hit Heinkels and Messerschmitts..... and the war turned against Adolf and his merry band of goose-stepping followers.
But you can't just introduce a new cartridge in the middle of a wartime situation..... and have no interchangeability with all those third-of--million existing rifles. So the rifles continued to be throated for that old-fashioned long, skinny bullet..... and the ammunition simply was MADE to shoot very damned well with the new 139-grain bullet, and we have the results today.
But whether by design or by accident, the 6,5x55 cartridge seems to WANT to shoot accurately. When you are working with it, you need a whole new definition of what is "good", simply because "bad" in the Swedish Mausers is what most people would call "good" in any other rifle.
It HELPED, no doubt, that when the Swedes modernised their old cartridge, they did so gently, dropping only 20 or so grains from the bullet. When the British did the same thing, they dropped from 215 down to 160, then back immediately to 174: 55 and 41 grains reduction PLUS shape change. The Germans dropped from 227 down to 154: 73 grains. And even the US dropped from 220 grains to 150: 70 grains. The Swedish development was the least radical of the lot, with MOST of the weight reduction obtained by changing the SHAPE of the bullet to a more-efficient form..... which could use the EXISTING throating. It was NOT a radical change but it WAS a superb improvement if you could guarantee that the ammunition was being used in good barrels..... and this the Swedes COULD do, thanks to their excellent maintenance program. Th "jump" from Chamber into Leade was not all THAT much...... and the long bullet was guided in a straight line by the mass of bullet in that long NECK of the Casing. And so the old long Throat WORKED.... because nobody got radical and made changes which would NEED a shorter Throat.
BTW, the final quantities of original Swedish 6.5x55 slugs, the ancient round-nosed types with the slightly-expanded flat bases, were disposed-of in Canada by Ammo-Mart back in the 1970s. You sometimes run into a bag or so at gun shows. I know that friend Buffdog is planning on running a test with a bag which I gave him.... but he has to get his house nailed back down first: they were hit by a tornado last week, left millions in damage in a town of only 250. So he is very busy right now. Later, though..... I have high hopes.
But it does seem that a Swede Mauser is GOING to shoot. It just wants to be FED.
Hope this rambling mess makes sense.