How do you know how much gas your gun needs?

[taroslice]

Im never too sure how much gas my GBB needs...

Do you just keep putting gas in until its full.

And after you've emptied a mag, is it okay just to refill it with BB's and continue until no gas is left?

And is it normal for it to fire blanks every so often?

 

[Rock-climby-Dave]

yes, yes and no, in that order