There are two small projections on the lower part of the ejector which push the cartridge forward. It appears that the left one is catching in the primer pocket when the rim is about halfway up the feed grooves, preventing it from rising farther. If I retract the bolt, I can slide the round on up the grooves easily with my finger or a screwdriver. I measured the rim diameter on the two brands of cartridge I had available. One measured about .503", and the other about .508". SAAMI spec is .514", according to COTW. I suggested to the owner of the rifle that he take his calipers and see if he could find some ammo with a larger rim.
Is this a common problem with these rifles? The rifle in question has not been fired much at all. It is virtually like new.