Sorry if this has been posted before, but I just figured this out and thought it might help someone.

I bought a Kahr CW380 a little while back and 300 rounds of Fiocchi ammo to do the break-in.  Well, I finally got around to running it through it and found that the rounds failed to feed 100% of the time.  They would not strip from the mag during firing, using the slide lock or slingshotting.  Most of the time they would lock up such that I couldn't slap the slide back into battery.  I checked online and found several posts on the Kahr forums that indicated problems with this ammo.  Sadly, the Fiocchi Extrema ammo also does not feed in the gun.

So, when I got home tonight I decided to see if I could fix the rounds.  Since these are pretty standard round-nosed FMJs, I didn't feel that bullet profile was an issue.  I figured it was either COL or case mouth bell getting it hung up, so I reseated a couple rounds to the same COL as the Remington rounds that were feeding well (I fully understand the pressure implications of doing this).  At the same time, I very slightly increased the crimp.  While I was setting up to do this, I got an indication of the real problem, but I went ahead with my changes.  The rounds refused to chamber.

So, the clue that was given to me was when I put the rounds into the shell holder.  There was resistance with both rounds and I had to press to get them into it.  The second clue was when I tried to chamber the rounds, I noticed some deformation on the headstamp where it was pinched between the extractor and the breach face.  This led me to check the thickness of the case rim, I found that the Fiocchi cases are .045" and the Remington cases are .035".  Further testing by filing the case rim showed the Fiocchi brass to become slightly more reliable at around .042", which is where I stopped testing.

I feel that this is not a problem with the extractor or any other part of the gun, but a problem with the ammo.  I say this because the cases also do not fit properly in a standard shell holder.

Also, FYI, the Perfect 380 ammo that Wal-Mart sells is absolutely the same ammo as the Fiocchi 95gr ammo, so if your gun won't run with Fiocchi, skip the Perfecta.  The cases are exactly the same dimensions, and if you couldn't see the headstamp you'd never be able to tell them apart.

Hope it helps someone.

This is interesting.

I have fired Fiocchi in 2 different .380 pistols, with no problems.  

One was a Colt Pony, the other was a Remington 51.

But, that was maybe 14 years ago, new production might have changed.

I'm guessing that the rounds run fine in some guns due to differences in tolerances as well as "break-in".  It's possible that the Kahr will run these rounds better after the 200-round break-in, or more like 1 - 2000.  With a little filing work I think that they would also run, but I'm not willing to try it on a new gun to run some cheap ammo.  Even if it's $100 worth of it.

My SIG P238 runs Fiocchi, its just not as accurate as other stuff for me so I dont buy it much. This was about a year ago, weird. Call Fiocchi and let them know...

That is very strange. In 380, Fiocchi is my first choice in ball ammo. It hasn't worked in everything but I have had good luck with it.

I've tried Fiocchi in 3 Walther PP series pistols series pistols, a Kahr CT380, a Glock 42, and 2 Browning 1911-380 pistols. I've had no problems with it in any of these guns.
OTOH: A Smith & Wesson Bodyguard did have trouble with it.

The 380 ammo that has caused me the most trouble is Winchester white box 95 grain flat point. The Walthers and Brownings choked on that load.

.045 appears to be the maximum rim thickness per SAAMI specification:

http://www.saami.org/pubresources/cc_drawings/Pistol/380%20Automatic.pdf

As noted above, it sounds like the rim thickness is within specification.

I don't have any Fiocchi loaded ammo in .380  ACP at present, but I've used in the past in a variety off .380s  (two Walther PPK/S pistols, an FEG APK9S, an FEG AP9S, and a Kimber Micro).  I also  uses Fiocchi brass in the same pole as all of the rest of my .380 ACP brass and it works fine in hand loaded .380 ACP ammo as well, and I've never had any issues with the rims not fitting the shell plate on my 550B press.

Given that, even with the shell holder issues, I suspect the issue is at least partly due to the snug extractor dimensions on your pistol.

Thanks for all of the replies.  I totally agree that the extractor fit is what is keeping the ammo from feeding reliably, although I still suspect that it's not out of spec.  The rim is particularly difficult to measure with my mic, so the .045" is the average that I could get.  The best way to measure it would be to actually cut one down.  

I am not a member on the Kahr forums, but I found many posts indicating that the CW380 does not feed Fiocchi ammo.  I contacted Kahr and they just gave me the "we've never heard of this issue" reply.  Hopefully it saves someone buying 6 or 8 boxes of ammo like I did.  I guess I got spoiled by my "big" guns feeding anything on the shelves.

My Mustang has no issues shooting this ammo.

Just came back from the range and this ammo was still 100% FTF for me and had feeding and ejection issues in a Glock 43, although at a much lower rate.

Wifes g42 has no problems with fio ammo.  She does have to have a solid grip though with any ammo.

Otoh, to get it to cycle 100 gr plated bullets I had to load it over published max loads.

Glock 43 is 9mm. That could be the reason or were you using a Glock 42?

Just a typo ;)

Roger that.

I bought 2 boxes of this stuff several weeks ago, looking forward to seeing how it does in my LCP.

This stuff goes about 3/4 of the way in and then needs a "push".  When I rotate it in the shell holder it will kind of pop in/out or drag at certain points, so I believe that it is not uniform in thickness and/or not concentric somewhere.