Be careful with your nomenclature! Ammonium nitrite and ammonium nitrate are two different beasts!
Which are you talking about, AWK? Nitrate or nitrite? He asks about the nitrate, and you seem to be speaking of the nitrite...
Although ammonium nitrite is not explosive, ammonium nitrate can be. Jdurg is right, it does take some energy to get it going, but it can explosively decompose upon strong heating, so you need to be careful. You do not necesarily need a cap to get it going either; just look at the 1940's explosion in Texas to find that out. Of course, that was an extreme case, but you don't need a cap to cause detonation--just to get the maximum output.