I have 3 for my KJW Beretta, which seems to be enough for the 45 minute games at XT in Winnipeg (unless there are a lot of people and I need to use it for suppression).
5 is the most I've ever used in one game.
This of course depends mostly on your style of play, however, Ive seen people use less or more than that.
3 (2 plus what it comes with) is probably good number for an initial purchase- it will force you to learn without leaving you at a real disadvantage.
Also: invest in a good dump pouch. Watching your mags hit a concrete floors sucks.
Edit: Never ever ever lend your pistol to anyone. No matter how pleasant or experienced they are it just invites the wrath of the GBB God and bad things happen.
Last edited by Cliffradical; February 10th, 2011 at 16:17..
Reason: Missed a good point