A popular SAAMI myth concerns brass thickness of military 5.56mm cartridge cases. SAAMI says military cases are thicker than commercial .223 cases. i've weighed thousands of cases since 1968:
US 5.56mm military cases are not thicker.
Some Brit military cases are thicker than US military cases. The thickest cases of all are Lapua; one must be careful when reloading those.
Click on brass weights comparison:
http://ar15barrels.com/tech.shtml