Because, at least on the Sav 10/110 platform, the extractor and ejector work somewhat in tandem. Or perhaps more accurately, the extractor *can* affect the operation of the ejector.
If the extractor merely hooks the rim, it will 'extract' the case from the chamber. But unless it's somewhat bottomed out in the case extractor groove against metal, when the case is withdrawn far enough that it is no longer supported by the chamber i.e. into the larger area of the bolt raceway - the ejector will push the case further to the side, and the *extractor* will lose it's grip on the rim, and drop the case. Pretty much exactly as the OP observed.
Sometimes, just replacing the factory 0.125" detent ball with a 0.140 (9/64") ball from your local Ace hardware store will keep the extractor piece centered up better in it's groove in the bolt face, and solve the problem.
Sometimes undercutting the lip on the extractor helps as well, as noted by others.
Sometimes the brand of brass comes into play. If you look at the SAAMI drawings for the diameter of the case extractor groove, it shows as "0.409 -20", so 0.389-0.409. The vast majority of brass that I have in my reloading stash - Lapua, Federal, Remington, Winchester, Norma, etc. measure between 0.403 and 0.406, across all brands. Except Hornady. The Hornady 6.5CM brass I had meaured between 0.391, and 0.397 - so technically within SAAMI spec. But in my testing... under 0.393", and it wouldn't eject, but drop just like the OP described (which is why I asked
@spudgun if he was using Hornady brass). Every time. Over 0.395", it ejected reliably. In between... maybe yes, maybe no, depending on how you stroked the bolt and if you were just lucky or not.
Savage did take some measures to address this on later guns... my original 12 LRP had the same extractor/ejector as my 12 FTR and F-class guns. But my later 10 BA Stealth has a different ejector and extractor. IIRC, they found that the ones they had worked out for the short/fat .300WSM solved the problem - the extractor is cut slightly differently, and the ejector pin has a beveled cut to the face, and extends further. Brass pretty much just flies out of the gun, like it should. Still uses that stupid 0.125" ball, rather than a 0.140... so it can still be 'improved' a little there.
Yes, the wire spring that Savage uses for the ejector seems notoriously weak in that it takes about one good hit from a hot load and it's done. Their solution? Put a tail on the ejector, so it can't collapse the spring, rather than use a better spring
