[StrongSideArmsInc]

First of all, its not the guns fault, and its not the ammos fault.

I have built 5 AR15 rifles in 7.62x39 and 2 in 5.45x39.

Wolf ammo is the culprit on this one. No, the ammo is not bad, it is made in the Tula aresenal in Russia and is of very good quality. However, the firing pin inertia needed to fire it is what is causing the issue. The fact that it is berdian primed, crimped and then coated with a sealer, makes it very hard to fire with a light spring set up in an AR type rifle. The Sig has the same issue.
When choosing springs for the AR, you must go with a set "red" springs for increased power and firing pin inertia. As imagined, you get a poor quality of trigger with the increase power.

Heres what I have done with good results:

First, I replace the firing pin with one that is made from titantium. The lighter firing pin travels faster and for the most part will shoot the ammo.

Second, I change the trigger system to a national match two stage trigger, I like Bushmasters set up.

Third, I have brased a steel pad on the front of the AR15 hammer, about 1/16th of inch thick. This increases the mass/weight of the hammer, and also increases the stroke of the hammer when it strikes the firing pin.

Now I don't know what options you have with SIG, but I am sure a comptent machinest/gunsmith can do the work.

I don't blame SIG on this one, the rifle works well. However, most people want to shoot low cost ammo, and you just can't have a good trigger system when firing Wolf ammo, unless you take the time to improve function of the weapon.

I think SIG was more inclined to have a nice trigger, why on earth would you buy a SIG and pay the money to have a crappy trigger, when you could have bought an AK to start with?

I have seen no issues with Silver Bear or Golden Bear. Not much higher, but a little softer primer, and better accruacy results.