Originally Posted By Remyrw:
The hammer spring accounts for most of the trigger pull feel in an AR, the trigger spring is really just helping reset the trigger after firing.
Assuming there was nothing wrong with your original spring and it was installed correctly, and you already checked for other causes for light strikes such as build up adding friction to the firing pin's movement then you either need to get different ammo or recheck things. A standard spring with an otherwise working rifle should not have primer issues with hard primers. Now, if that spring is softer than it's supposed to be, then you have a different issue, but you should never NEED an extra power hammer spring in an otherwise normal AR. Heck, most of us use LIGHTER springs and still set off mil-spec ammo reliably.
Maybe a drop of lube spread around on the firing pin before putting it back in the bolt after cleaning? Triple check it's clean in there and that your hammer isn't binding on the receiver's sides.
The sear is ground at a positive angle. Watch the hammer as you pull the trigger, it moves back against hammer spring pressure.