I think what Stealth means is to apply pressure upward from the bottom of your magazine.
You should push your mag up into the magwell, in an attempt to release the small notch that keeps the BBs in the mag until you want them out.
This way, you can test to see if it's the Rifle's problem or the Magazine's problem, and based on posts above, it seems to be the rifle.
__________________
[]]]]]]]]]]]]]]]]]
------)_'_\ * (
"----------\ * \
"-----------\_*_\
|