Originally Posted by doc_pathfinders
from conversations with a friend in HK, who knows his stuff..
'when the piston is retracted from the fully forward position, it creates a partial-vaccum infront of the air-nozzle, sometimes this partial vaccum is strong enough to pull a bb up from the HOP BB Feed tube'
some guns will create a greater vaccum (full-cylinders) then others, rate of fire makes a big difference as well as spring strength..
i would guess a stock (or near stock FPS) gun with full cylinder and a high voltage battery would generate the most..
I'm sorry that is a bunch of Crock. Being in HK does not make one an expert, I am dealing with a guy in HK asking a slew of questions to an international board where he could get his answers by going down to Mong Kok to see and ask the people in the stores (Been in airsoft for over 2 decades BTW).
AEG's are not an enclosed system. In no way is there ever any measurable vacuum effect. Not down the barrel or up from the feed tube. AEG's are in fact an "open" bolt system.
The reason why AEG's are dropped bb's is due to only one reason. Feed tube length. I always drop 7 rounds from my SR47...this is due to the long feed tube.
With the last BB leaving a standard or Midcap magazine, nothing is pushing the rest of the bb's up into the hop-up chamber. You will drop what is in the feed tube unless you invert the AEG.
With a Hicap, this occurs when spring tension is lost after the last BB passes the paddle spring. You get about 10-15 bb's in the magazine tube that can't get out and what's left in the feed tube. Unless, again you invert the AEG.
This is all normal. Only way your getting all the bb's to feed is if you have and use the TM AEG's that have the BB follower that stick out of the magazine like this:
Otherwise "dropping a few" is normal.