piston is solid on to carrier. I have AR180 tho
that isn't the piston: the piston is a small piece directly acted upon by the gas from the gas siphon / gas block. in the gas block assembly is the gas plug (turnable piece for takedown and adjustment) the piston (the moveable part that the gas acts upon with a piston ring to generate pressure and convert hydraulic motion into direct mechanical motion), and the gas piston spring which let's the piston return to the neutral position.
edit: that appears to be a 9mm conversion of the AUG, which may be direct blowback or short recoil operated and will not possess a separate gas system at all. doesn't appear to be locked breech either.
i have a 1986 AUG A1 imported as a reference weapon for film production (this particular SN was used in Robocop).
the fixed portion on the carrier is the operating rod, connected to the carrier. the piston is energized by the expansion of gas in the gas chamber formed by the gas plug, gas block, and piston. the piston violently moves a short distance rear-ward
striking the operating rod to transmit mechanical force to the rod and the bolt carrier assembly. this is the essence of a short stroke tappet gas system.
the whole shitting part ... depends on ammo a lot. Shoot some Barnaul shit and try cleaning "urethra" of that gas tube.
yes, ammunition quality varies greatly, that's also not what is happening. fouling is generally a combination of carbon and gliding particles (copper, brass, et c) that are carried by the gases from firing a cartridge. often these gasses will also have unburnt powder, powder residue, and primer compound (typically a salt, which can be corrosive or not).
the hot gases expand in in the barrel, carrying this fouling and as they expand, they push against the interior of the case in all directions, the bolt face, and the rear of the bullet. the "plug" formed by the bullet will travel down the barrel and eventually past the siphon in the gas block and exit the barrel. the gases though have a brief moment to
also enter the gas tube (path of least resistance). the amount of time between when the bullet is functioning to energize (pressurize) the gas system and when it exits and depressurizes the gas system is known as
dwell time. it is in this short amount of time that the pressurized system uses the expanding gas as a source of mechanical energy to drive the action: namely to unlock the bolt from the barrel extension and rotate (via cam) the bolt to unlock and allow the cycle of firing to continue.
when hot expanding gases travel through the hollow gas tube, through the gas key, and
enter the carrier, and create a fluid piston - this piston is formed by the expanding gases acting on the interior of the carrier (the chrome lined portion typically) and the
rearward portion of the bolt itself.
note the area behind the piston rings on the bolt. this expanding hot gases are immediately vented out the side of the carrier via 2 or 3 vent holes at high pressure, which is the majority of fouling gases.
during this act of depressurization, the bolt is forced
fore-ward by the initial expanding hot gases and the carrier itself
rear-ward. because the carrier is on a three rail track, it cannot rotate. the bolt is then forced to rotate which unlocks the action at the moment pressure is low enough to allow it in the barrel and fluid piston, but still high enough to move the assembly rearward with some help from recoiling action. the action spring is then compressed to catch the bolt carrier assembly as it completes unlocking, extraction ,ejection, etc and the cycle of fire continues.
thus the vast majority of fouling gases are safely vented through the side of the carrier and the hard chrome interior of the carrier is largely unaffected as it is scoured by hot gases on each shot. the last shot doesn't have a following "scrub" and this is what will eventually foul the interior of the bolt carrier. what little gas remains is from the barrel (which virtually all self loading rifles will have as a consequence of mechanical design) and it is
this gas and it's aerosolized carbon that can, with time, foul ammunition.
if you want to see what fouling gases would do to a case if they were directly exposed to the hot gases (which bakes on the carbon at high pressure and heat), look at something like a spent case from a G3 with a fluted chamber that allows gas blow by (fouled gas directly from the barrel). very very dirty.
there's some animation floating around that a troll incorrectly marked as how the internal modified direct gas impingement system works. it is entirely wrong.
