Was going to buy a drop in trigger for my Ruger ar15. Gun shop talked me into new springs. 250 rounds later, no light primer strikes. Shoots 3/4 moa at 100 yards. With scope, shooting from bench rest.

I tried the same with my Ruger AR556. Had tighter groups with premium ammo, but significantly worse groups with typical off the shelf ammo. No light primer strikes though, but I did bob the hammer. I used to get 2" groups with Winchester white box m855, but after the trigger changes they opened up to around 6".
I just installed a Geissele SSA-E trigger in it and it is really nice. But ironically I had two light primer strikes with it! And yes I've installed the hammer spring properly. No problems since so not sure what caused the two malfunctions.

I only shoot pmc 5.56. With new springs, very little trigger creep. Very smooth pull.

The light strikes are very atypical and must be ammo related.  The SSA-E uses a full power hammer spring.  The hammer is lighter to decrease lock time, but the spring is full milspec force.

I had light primer strikes with the jr springs using federal m193 and wolf .223.

Being that that was my primary ammo, I ditched the springs and went with a geissele.

I do strongly believe it's ammo related.