Lake City and commercial contract 5.56 ammunition made for the military is actually thinner "BUT" is made harder than commercial .223 brass.
Below our American Lake City brass has the "MOST" case capacity and no reduction like you have with "thicker" 7,62 brass is required.
This dates back to the Congressional hearings on the early jamming problem with the M16 rifle and one of the cures was to make military 5.56 brass harder. The reason being you could not make the case thicker and have enough case capacity for the required velocity.
How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshooter.com/2014/05/how-hard-is-your-brass-5-56-and-223-rem-base-hardness-tests/
TEST RESULTS
Using Rockwell hardness standards (.062″x100kg, Rockwell “B”), the brass measured as follows:
LC 2008 = 96
Lapua 223 Match = 86
Winchester 223 = 69
Remington “R-P” = 49
Summary of Test Results
Catshooter writes: “For all you guys that have believed that Winchester cases were tougher than Remington — you are vindicated, they are a lot tougher! However, Lake City and Lapua are ‘the pick of the litter'”. Catshooter notes that both Lake City and Lapua are significantly harder than either Winchester and Remington .223 brass. That’s something that we’ve observed empirically (Lapua and LC stand up better to stout loads), but now we have some hard numbers to back that up. Hats off to Catshooter for settling the hardness debate with his Ames Hardness Gauge.
For practical purposes the only difference in "some" .223 and 5.56 rifles is throat length.
I have two AR15 rifles and a Savage .223 bolt action with a 1 in 9 twist and the throat is longer in my Savage bolt action (.566 vs .500)
Also forget the NATO pressure of 62,000 psi it is measured by European CIP standards and the transducer is mounted at the case mouth. American transducers are mounted at the mid point of the case and both the .223 and 5.56 have a maximum chamber pressure of 52,000 cup or 55,000 psi.
Bottom line I buy a lot of once fired Lake City 5.56 brass for the cost savings and quality of this brass. I can buy 500 cases for fraction of what you would pay for 100 Lapua cases. So forget the myth that military 5.56 cases are thicker and have less case capacity.