Try doing a google or youtube search, theres lots of websites out there. Basically a gun that fires open bolt has a firing pin that is fixed in the bolt, the bolt slamming closed fires the round, gas pressure reopens the bolt and it is held open until the trigger is pressed again. Prevents the chamber from getting to hot after firing full auto.
"The budget must be balanced. The Treasury must be refilled. Public debt must be reduced. Arrogance of officialdom must be tempered and controlled. Assistance to foreign
lands must be curtailed, lest Rome become bankrupt. Citizens must again learn to work, instead of living on public assistance."
Cicero, 55 BC