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Could be that you need to set the shoulder back a bit. Try turn your die in another 1/2 turn and size a case......try the empty case in the gun to see that it chambers and extracts easily. Myself (and many others) have had this trouble when loading for the AR.

Quoted:
I suggest you buy a case gauge.

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Can someone help me out?  Im having a problem with some .223 that Im loading, they seem to be getting stuck in the breach, after the firing pin has hit, (they are lodged into the breach).  I might have slightly mashed the necks with the seating die, but I dont think so.  One thing that Ive noticed is that I dont appear to be crimping them enough, because I pushed a few of the bullets back when trying to get them unjammed.
Thanks for the tips.

Quoted:
I suggest you buy a case gauge. That will allow you to see for sure if your resized cases are in spec in terms of headspace and length.

.........IMHO…………"the secret" to re-loading a bottle neck cartridge for a gas gun is to gauge your re-sized brass. There are many different brands and ways to gauge your re-loads.  

Examples……..

http://www.sinclairintl.com/cgi-bin/category.cgi?category=REMTHT&type=store

This is how I do mine.

6) I use a single station press (RCBS Rock Chucker). You could use a progressive Dillon IF you wanted to. It's a personal choice. But, with whatever press you choose, consider shell plate/shell holder and/or press "flex.”  I use a regular FL size/de-capper die, NOT the small base dies. To begin, lube your cases.  Then, FL size and de-cap, 1 or 2 cases for a test. Gauge the re-sized case(s), to confirm that the "correct size" has been achieved.   I use a Forster Products case gauge (the Wilson or Dillon case gauges are also popular choices).  Insert a case into the case gauge.  The headstamped end of the case, needs to be at or between the high and low cuts on the gauge, to pass. This checks the headspace.  While the other end, is used to check if the case will need to be trimmed (a job for later on).   IF, it’s not the “correct size,” your die setting will need adjustment. Lower the ram and simply screw the die in or out a little. Don’t forget about the lock nut. Then, re-size another couple of test cases and check your work again. Repeat the test and adjustments, as needed.  When you're satisfied that your test cases are properly re-sized, do the entire lot (remember to test some cases throughout the run).

What you do, or don't do, is up to you.

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If you are already close with your resizing setting turning the die another 1/2 turn is way too far. That's why gauges are a requirement. Nobody should be guessing at their headspace settings in this day and age. 30 years ago you couldn't locate a case gauge other than the most rudimentary style. Nowadys they are everywhere. It's a got to have item.