My 84M's in 260, 7mm-08, 308 and 243 feed very well. However if one loads the box with very long handloads say at 2.810" then they are subject to the meplat catching on the front of the magazine box. As you know most boxes are just flat on the top edges.
It's the second round down that catches. I have to load them by pulling each round back as I load it and then they go down ok.
Recoil might force the second round forward and cause it anyway? There was a video here of a 84M that would jam. He sent it back and they said it was ok. He sent it back again and I have not heard what happened?
The problem is that the second round tips with the base of the round down and it lets the base of the top round drop as well and the bolt rides over the rim making a jam. It happens quite often to me at the bench as I like to do the testing by feeding them out of the magazine and due to the angle of my hands etc. I don't load them all that carefully as its just the range. Sometimes I have to stand up and push them down and back and then they feed. I might file the inside edge of the magazine box to a smooth taper in the front.
I am quite sure this is the problem. Of course it could happen with other rifles as well.
There are two rounds in that magazine and the one underneath is catching on that sharp right angle edge of the magazine box.