The Model 670 is a cheapened down version of the Model 70, with a plain stock, no magazine floorplate, and a finish that is not as polished as the standard Model 70. The Model 670, AFAIK, was made only post-64, which means it uses the new bolt head and sliding extractor, not the Mauser style of the pre-64 Model 70. Those extractors are even more prone to problems than the old style and if the case is not gripped well, the plunger type ejector will push the case out of the grip of the extractor, just as Mr. White says.
In most cases, the problem is dirt or grease interfering with the extractor side movement or dirt or grease in the extractor plunger hole in the bolt. One answer is to use a good spray cleaner (I like G96 Gun Treatment for this sort of thing, but other cleaners will work) around the bolt head to free up the extractor. If that doesn't work, the extractor can be removed by using a small punch through its hole to push the plunger in and slide the extractor out to the side. (This is a good way to lose the plunger and spring, so be very careful!) Then the extractor slot and the plunger hole can be cleaned thoroughly and lightly oiled.
Jim