I did the same as you and got the same results.
With a little practice and experience, you will know when your mag is empty if you don't hear/feel the twang when shooting long fast strings of fire.
Just one of those things.
Assumption is the mother of all ****ups.
Know what you know, Know what you don't know. -Paul Pedzolt
"Jack of all trades, master of none, though oftentimes better than master of one" -Mynshul