[dpvu]

If there's no cloud or harder kick and no leak that means that there is physically less gas in the mag for whatever reason. When filling, there shouldn't be any gas escaping out around the adapter/fill valve. That means it's full or you've got a bad connection.

I know the FAQ says that 6 is generally the max but I know some people fill until it's full (gas spewing out the valve). This is probably going to start a "How to fill a GBB mag debate" but I've filled this way and never blown seals. My KWA manual actually says to fill until gas overflows from the valve. On some guns this won't happen and you'll have to listen for the sound of the gas filling to stop.