I have a Ruger American Ranch in .450 Bushmaster.  I shoot Winchester Deer Season XP Extreme Points out of it and have had no issues until a couple of days ago.

One round would not eject.  I thought it was my extractor, but other rounds have ruled that out.  Its only this one round.  I didn't try firing it, and brought it home instead.  I took a micrometer to it, and the rim is slightly larger than some, but not bigger than others that cycle just fine.  I can't find my calipers and, am not sure they could get in anyways to measure the thickness of the rim, but it doesn't look any different, some are a little thicker, some a little thinner.  OAL is consistent with ones that cycle just fine too.  Depth of the groove looks fine as well.  I can get it to engage the extractor when I have the bolt out, that doesn't seem to be any different than the other rounds either.

Wondering if there is something common I'm missing here that's leading to this or should I contact Winchester and see if they want to look into it.

This is a picture of some of the cartridges.  One of them is the culprit.  Does anyone see anything I'm missing?

Hard to tell from the pics, but the 5th one looks like there isn't enough of a step for the extractor to grab.  Edges look rounded too.

I would download a SAAMI chamber/cartridge drawing for your cartridge and start measuring your cases to it you will find the issue pretty quickly I bet..most likely the case diameter just above the case head isn't sized enough on that case for some reason..Oh, and my guess is the middle cartridge of the 7..it looks like the body of the case has been dragging on the chamber walls...

You win the prize!  It is the middle one, and I noticed as well that it was getting marked up a bit.  I'll have to measure above the head and compare it to the others.  I thought it would be more about the rim, and not the case itself as it seems to go into the chamber fine.  

Any idea if it would have caused problems if I had fired it?


**EDIT**

Just checked it, and its the same diameter just above the extractor groove as the others, and same with further up towards the bullet.

My guess is the bevel above the slot for the extractor is off.  This would hold the extractor out just enough to miss.  I would polish the extractor, if it were mine.  YMMV

Hmm, got a bore scope OP?, I wonder if it has a carbon ring built up in the neck area and certain rounds are longer from case head face to neck(trim length consistency), which is just enough grab to make the ejector come off the rim..I would bore scope it/measure case over all length carefully and/or clean the living dog piss out of the chamber and see if it goes away...

Ever figure this out? My guess is that the case is just enough shorter that the bolt can’t grab it well after it plunks, since its a straight wall case that headspaces on the mouth.

Anybody else notice the center one is leaning?  This suggests the head is not square to the body.  Try it several times by turning it in the chamber.