Frog Stealer, I recently fixed a 404 Jeffery M-70 conversion rifle that had the exact same problem you are having with your rifle. To fix it I cut the tabs off the of the magazine box, this modification to the box allows the bullet noses to spread out just enough so the cartridges will stay under the feed rails when the bolt is cycled back either forcefully or gently. With the magazine box removed from your rifle you will see two vertical sheet metal tabs that project vertically. Use a dremmel tool with a cut off wheel and remove those tabs, debur the edges with a file and reassemble the rifle. The rifle I fixed was done by some other Smith I can't recall his name at the moment, not that it matters much. When looking at the M-70's there where three versions of the ultra mag actions, the main differences in them was how the feed rails where machined at Winchester. The first version had straight rails with out flared openings in the rails, the second had just one flare on the left side and the third had rail flares on both sides. The first version was the best action for doing a 404 because no flares means more rail metal which means the cartridges stay under The rail until fed.