Originally Posted by jmart
The port will see the high pressure unless it's bled off earlier. In so doing, you'd need to bleed it off and vent it out to the atmosphere, you wouldn't want to direct it back to the BCG. But in so doing, I would expect velocity to take a hit.
The amount of gas that gets directed back to the BCG is related to the port diameter. Make it too small and you won't send enough gas back to cycle the action. Make it too big and the system is overgassed. Run your weapon hard and that gas port, which was properly sized when new, will erode and enlarge. Over time it will send more and more gas back to the BCG.
New weapons cycle around 650-750 rpm IIRC. As the port erodes cyclic rate can jump to over 1,000 rpm. That's where things start to get dicey WRT reliability.
I wonder if someone has ever concocted a bleed valve arrangment to regulate port pressure? if so, where did they vent the gas, forward maybe? I also wonder why the M4 designers haven't designed an adjustable gas valve to regulate the amount of gas directed back to th BCG. I'm pretty sure JP and MGI both make adjustable gas systems, but I'm not sure how effective and field-adjustable friendly they are. I think if someone could make one that could be easily adjusted in the field, that would be a huge boon to the M4 system.