Hi, bigedp51 here and putting an end to rumor control and its wild misinformation.
In the photo below on the far right and left are Lake City brass and the web area at the flash hole is much thicker than the Federal case in the center. "SOME" batches of Federal cases have the thin web area and have a bad habit of the primers falling out when these cases are again loaded on the warm side.
Google is a wonderful tool for getting and learning information, forums are good for spreading rumors and misinformation.
Alliant Techsystems Inc. (ATK) has the contract to make ammo at the Lake City plant for the military. Federal is part of ATK and they make "military type" ammunition at their civilian Federal ammunition plant. "BUT" some of their brass is made to .223 pressure standards and is "NOT" mil-spec grade. Also you will see two different loading pressure standards at some websites for military and civilian loadings.
If you mix military high pressure loads in softer civilian cases you can run into problems, and most of these are popped primers jamming the trigger group of your AR with the brass ending up in the trash, end of story. I reload my ammo to pressures below both standards and my brass loves me, my rifle loves me and in most cases when you shoot a zombie in the head they don't notice the difference either.
On a fired case the rear end of my vernier calipers will fit in the neck and you can get a thickness reading in the web. If the rear end of your vernier calipers will not fit in the neck then cut a two inch rod that will fit the neck and measure using the rod checking for web thickness. I know this because I have three five gallon buckets of .223/5.56 once fired brass and after sorting by head stamp I prepped the the "wrong" Federal cases first. On the bright side now I have prepped Federal cases I can use for reduced loads once my sore fingers stop bleeding from removing all those crimps and uniforming all those primer pockets. (and making the web area even thinner) :'(
The problem started during the Viet Nam war and was just one of the many causes of the jamming problem when the M16 rifle first came out.
.223 vs 5.56: What’s the Problem?
ftp://ftp.fwpubs.com/Outbound/Direct%20Brands/GD2013_AR15.pdf
There is 10,000 psi difference in chamber pressure between a .223 and the 5.56 cartridge. And mil-spec 5.56 brass MUST be harder and stronger than commercial brass to withstand the higher pressures and larger military chambers. And if the case does not have the NATO symbol stamped on the base, it does not meet military standards for hardness and pressure.
5.56 vs .223 – What You Know May Be Wrong
http://www.luckygunner.com/labs/5-56-vs-223/
And to make up for my sore fingers from removing crimps from thin Federal brass.....................................
Eat your hearts out, the Remington .223 five gallon bucket is missing in the photo, and isn't crimped.
And the Remington brass is used for my Zombie loads. ;D