there are so many different factors that go into how big your load is. one is how turned on you are; if you've been edging or not; how long ago your last orgasm was.
as for your second part of the question, there is no "normal" amount in which one shoots. hell, most guys aren't really much of a shooter anyways. but i believe the average amount of semen per ejaculation is about 1.5cc - 2cc (1.5ml - 2ml)
honestly, as long as you're not shooting blanks, you're fine dude. and, if you're concerned about your sperm count, go to a sperm bank. they measure stuff like volume and sperm count