Swedish Mauser reloads key-holing!?

[Parashooter]

It's probably not a lube groove but a "dirt-catcher," designed to give fouling left in the rifling grooves from previous shots someplace to collect without being mashed into the first groove-diameter band. This is a common feature of bore-rider designs going as far back as the black powder era but not really needed with smokeless. Here's a typical example dating from the early 20th century, Lyman/Ideal 311332 -



What's odd about the 6.5 bullet shown in this thread is the apparent step in the forward band - probably from nose diameter to base diameter. Putting a dirt-catcher in front of such a conical step is questionable design. Note that Lyman's 150-grain 266673, below, has the step but not the forward groove.