This can sometimes fool you. I've been told that high speed imaging at the factory has demonstrated how a tight extractor, or heavy extractor spring (or both) can often cause the case rim to bounce down and away from under the extractor, which might give someone the impression that the case never reached the extractor ... when in fact it did.

I learned this when discussing diagnosing potential feeding issues with someone in pistol repair at the factory one time. This was one of many things they took into consideration when examining pistols sent in for "feeding problems".

BTW, I did have a 4513TSW one time that was experiencing a repeated feeding problem. It was only a couple of years old. I discovered one of the mag springs had been installed backwards, but that didn't resolve all the feeding issues. The recoil spring set was a somewhat shorter than a new set, but replacing them didn't completely resolve the problem, either.

Neither did adding some needed lubrication (insufficiently lubed, but not dry). Still a couple of feeding stoppages.

The next thing I tried was checking extractor for fit and spring tension using the appropriate gauges. While the extractor appeared reasonably clean enough, I found that it required some unexpected effort to insert one of the gauges (flag gauge) all the way between the extractor and the breech face under it, as well as the other gauge between the hook and the opposite breech face shoulder (even though it cleared the bottom of the hook and partway up the hook as it should, indicating it wasn't too tight). When I checked the fit with those tools a lot of hard carbon fouling was removed from the breech face and from under the extractor hook. The gauges were now easier to insert. The extractor fit & tension was well within normal spec ... except now the gun ran as it was supposed to run without any feeding problems, in both my hands and the user's hands (issued weapon). We couldn't get the gun to fail to feed, and I even relaxed my grip and wrist lock when test-firing it for several mag loads.

Was it just one of those things I observed and addressed, or all of them to some degree, contributing their influences to the number of feeding stoppages (since the frequency of feeding problems decreased a bit as I addressed each thing to some extent)? Which was the possible "major cause"? A subtle combination of all of them? That's where I put my best guess ... but the important thing is that gun ran right and exhibited the expected excellent feeding & functioning when I was done, and we couldn't make the gun fail to feed.

That hardened carbon fouling was very difficult to see under the hook. I keep a brass tool with a narrow square edge (I can keep square with a file) to clean out the carbon in places like that nowadays. I don't like using steel "dental picks" against steel gun surfaces, FWIW. I was lucky when I used the extractor gauges because they were designed to move along the surfaces when the parts were fit in the right spec (the GO condition) without damaging them, although the flag gauge is no longer used or sold to armorers. I was told the extractors are being produced so that the dimension checked by the flag gauge is no longer a problem to concern armorers.

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Ret LE Firearms inst & armorer