I"m new to ARs, had one about 1 month and I'm wondering why they don't have a firing pin spring to keep that nasty looking pin off of primers as the bolt closes?

Just wondering because most of my arms (pistols and shotguns) certainly do have 'em.

thanks in advance..ECS

 On a military style rifle the firing pin usually rests very close to the primer, less travel equals sure fire ignition.  It is common to see a very slight mark on the primer of a chambers but unfired round.  No spring, because one is not required, the hammer strike makes it go bang and it typically does not have enough inertia to go bang without the hammer strike( the bolt and bolt carrier moving into battery eats a lot of that up).
 Beside it is one less part for the average grunt to drop in the dirt and never see again.  Follow you assembly instructions to the letter, never fire an AR/m16 unless you have the bolt and bolt carrier correctly assembled and installed.  Get help if you are not sure.

You need to pick up a spring at a gunsmith shop.  Your AR15 won't fire right unless you put a 16# spring in the carrier!

Spring is not needed.Check out how the AR/M16 works,Stoner used K.I.S.S. for the GI's.

Lonegunman has it right.  Many military rifles don't have them (M14, Garand, etc.).  Just make sure you ALWAYS load from a magazine.  The recoil springs are designed so that the bolt carrier has enough forward momentum to strip a round from the magazine feed lips and then chamber it.  If you just drop a round into the chamber and then let the bolt slam forward, the firing pin can move forward with enough force to cause a slam-fire, which is bad juju.

The primer cups on the commercial primer are a bit thinner than the mil-spec ones.  I believe there was a discussion of this subject at the Fulton Armoury site, WWW.FULTON-ARMORY.COM.  CCI makes some mil-spec primers, but since you don't have a problem with slam-fires, this is just some FYI.