Fundamental misunderstanding continues. The G18 achieves auto fire differently than a G17 with a switch does. The trigger bar isn't "held down" in either case, though.
Most are already familiar with the M14 - it's the disfavored stepchild of US military rifles, and it's shortcomings left it as a stopgap between the M1 Garand of WW2 and Korea and the AR-15s the US military has used since. 
Passed in 1986, the Firearms Owner Protection Act (FOPA) was staged to be a massive victory for gun rights - establishing a way for guns and ammo to travel interstate, even in states that restrict or ban their sale/possession. This allowed ammo to by mailed as well.
The edgewater buffer (actually listed as a spring guide in parts lists) was meant to cushion the impact of the bolt on its rearward stroke by using a series of stacked discs. However, when exposed to rain or debris, the rings could stick together, and the spring guide would become a rigid post instead.
223's history dates back quite a ways, but in the interest of clarity, I'll leave out some of the details of early military experiments with small caliber rounds, and start with the "Small Caliber High Velocity" (SCHV) program.
Gun import laws shouldn't exist, not even for sanctioned countries, but unfortunately they do and the relevant three letter agencies care way too much about monitoring this sort of thing.
Dang judge, you really think so? Well you said it, not me! 
The M16's reliability was very clearly traced to the use of powder design for 308 in the new 223 ammo being used. The 308 powder was much slower burning, and caused cases to stay sealed tight in the chamber during extraction.
This thread is quite long, so I'll summarize some key points:
"People might learn about Rhodesia because of this video and become racists" it's a wonder how your puny brains remembers to breathe