There are likely 2 issues:
1- You need to either put in a magazine block or silver solder rails into the magazine just forward of where the shoulder of the cartridge sits. This is because the action was designed for longer cartridges with more taper. I had similar issues with my 22-250 until I put in a magazine block (a block of metal at the rear of the magazine to reduce the volume of the magazine and make the cartridges sit farther forward). Each M98 is slightly different, and there is no "one size fits all" answer.
2- Polish the feed rails so the cartridges slide easily across them. Do not remove a lot of metal, just polish them. I use a stone on the feed rails when I build Mauser 98s, but some 320 or 400 wet/dry paper on a small dowel will also work.