Sounds like you do need to polish the feed rails, if you don't want to buy a set of stones get some wet/dry 600 and 800 grit sandpaper. Use a light oil with the sandpaper when you are polishing. Go slow, take your time, and check about every 30 minutes to see how your rifles are feeding.
It's tough to get the geometry right with a short stubby cartridge like the 243 in an m98 action, but it can be done with patience (my brother did it with a Turk M38 action and rethreaded Remington barrel).
Machine guns are awesome until you have to carry one.