If you had a weapon with a cyclic rate of 550 rounds per minute and you fired it continuously it would take you over 332 years to fire 1.6 billion rounds. Powder does not last that long and the rounds are subject to other forms of deterioration.
So much misdirection! ... The fedzilla is buying a multi year supply of ammo (and nearly everything else it will need) because they know there is coming a date certain beyond which they will not be able to be resupplied while the collapsed nation rots under starvation, disease, and mayhem, reducing the population to the ‘manageable’ levels called for in agenda 21.