I woudl almost suspect the hopup rubber is torn or otherwise damaged. If you are saying there is more air comming out of the feed tube in the mag well then the end of the barrel then there is something in yoru barrel assembly that is blocking air.
Take the barrel out of yoru gun and look down it to see any obstructions. If there is no obstructions, you could try to check that the tappet plate is locked onto the air nozzel correctly. if it's not then the nozzel might not be going inside the hopup all the way and thus not making a good air seal to fire off the bb's.
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