As reloaders we are all a bit cheap and when it comes to brass we like to use everything we can get our grubby little hands on. However this can occasionally be to our detriment as reported on other reloading forums and sources.
One case in point seems to be
Federal FC headstamped .223 Remington brass. This common brass that is available in both Federal and the loss-leader American Eagle brands has a couple of characteristics that can be less than desirable when it comes to reloading. In fact, they can contribute to either
over-pressure or perhaps a
case-head failure in certain circumstances when the brass has been reloaded a few times. Late '90s FC seems to have been the worst offender, but avoiding all FC would be advisable. Be aware that Federal has also been known to use high quality LC military headstamped brass in their American Eagle line as well, and that is good brass - SEE CONCLUSION #1 BELOW. Also be aware that in chronographing, reloaders report that AE factory ammo is a bit slow, indicative that it is loaded to less pressure and for good reason.
FC cases have less case capacity. This is because FC cases have a thicker case wall than any other brass manufacturer. When measuring case capacities of different brass, most common commercial (Winchester, Remington) are very similar to Lake City (LC) and WCC military brass. However, Federal commercial has a lower case volume.
When a hot load is worked up in other brass, and then that same load is used in FC marked brass, over-pressure is more common because of this lower volume.
FC cases, when cross-sectioned
show thinner webs, and thicker case walls. See the photo below illustrating the difference between FC brass and military or other commercial .223 brass.

FC 07 left / FC 223 center / LC 08 right The center FC 223 with the thin web is not safe to reload IMO
Mil-Spec FC 07 is the same as LC 08 and both are good.
CONCLUSIONS:1. The old Federal Eagle made before ATK took over operation of the Lake City plant has a very thin web surrounding the primer cup. Most reloaders consider this brass good for one reloading, then the scrap bucket. The primer pockets are too loose to hold a primer after the second firing.
Now that ATK is operating Lake City, Federal Eagle brass is showing up with LC on the headstamp (since about late 2006 or early 2007). The assumption is that it has dimensions identical to pre ATK brass made when Winchester operated the plant, but I haven't seen a cross sectioned case to confirm whether that it true.
2. Separate all FC headstamped .223 brass from your other headstamps.
3. If a load has been worked up in other brand or military .223 brass - reduce load and start all over again if you just have to use FC brass.
4. DO NOT use FC .223 brass for maximum loads. If you have to use it, save it for reduced or plinking loads.
5. Be aware that the thin web is a ticking time bomb and using FC .223 brass over and over again is not advisable.
6. If at all possible, avoid picking it up, or just throw your, on hand, FC .223 brass away and save yourself a possible headache down the road.
IF YOU WANT TO CHECK YOUR FC HEADSTAMPED BRASS - HERE IS A THREAD ON HOW TO DO IT FROM AR15.COM :www.ar15.com/forums/topic.html?b=6&f=42&t=276154&page=1