Heh, heh, one of the "tests" that is applied to any weapon being considered for military use by US Troops is the "Mud Test" . .
They completely wallow the test weapon in a tub of medium to fine mud at a viscosity of about 90 weight, clear the action with an index finger, insert clip, clear again, close bolt or reciever and shoot (or try to). After the M-14 and the M-1911 I have no idea how anything the military bought and issued ever passed such a test. But that will explain why most military actions rattle when you shake them . . And it explains why an AK will work after being dipped in 4" slump concrete!
And you're right about the "Full Length Resize", especially in the higher dollar AR style rifles and carbines. The early cheapies and the second gen issue M-16s all had such loose chambers that anything close to 40k of pressure would tend to split cases at either the shoulder or the cartridge base, but today's rifles all need a pretty straight cartridge because the clearances are so much closer, both from manufacturing abilities and the need for accuracy.
Way back when I was a Range NCO at Camp Roberts, CA, we were host to the Sixth Army Rifle Team and their "match grade M-1 Garands" . . There wasn't a rifle among them that would have worked if it was even dirty from repeated firing, let alone mud and dust, but they were pretty pieces . . and they worked very well at what they were used for . . . Most of the shooting they did down there was 1000 yards with iron sights . . !