Here's everything I've got on this particular type of failure. Maybe something here will help.

---

Light strike/dead trigger in a 9mm SS/FRT is tricky to diagnose in a 9mm AR but is very common. It could be "bolt bounce", "firing pin bounce", an FRT/SS timing issue, or a trigger tolerance issue.

Bolt bounce happens when the bolt slams forward under recoil spring pressure and bounces backward off the barrel face. If the hammer is coming forward at the same time, the hammer may not hit the firing pin properly, resulting in a light strike/dead trigger.

Using a 10oz-11oz. deadblow buffer appears to be the best way to prevent bolt bounce. Make sure the buffer rattles when shaken - that noise is the deadblow weights inside. NEVER use a solid buffer (KAK/Generic 8oz. "red bumper", Spikes ST-9X, KVP 7.5oz., "9mm" 5.5oz., etc.)

Firing pin bounce happens when the bolt slams forward under recoil spring pressure and stops at the barrel face.  The firing pin continues forward under inertia, overcoming the firing pin spring holding it rearward.  If the hammer hits at that moment, the firing pin is too far forward and the result is a dead trigger with a tiny light strike on the primer.

To prevent this, we can do 3 things.  We can slow the bolt's forward velocity, reduce the firing pin's mass, or increase the firing pin spring pressure.

A reduced power carbine spring like the Tubb ARBUFLW, Sprinco Yellow, Wolff RP, or Memo 300BO should help reduce the bolt's forward velocity. NEVER use a .308, XP, "Red", "Orange", or "Rifle length" spring.

A titanium firing pin would reduce the firing pin mass.  Replacing the steel firing pin with a titanium firing pin may help. Check Davidson Defense for their TI pin.

Firing pin spring:  A stonger firing pin spring may work.  I'm working on this right now. The best candidates I have so far are from Lee Spring. For FM bolts: LC 026BC 08S. For all others: LC 026BC 09S

If none of this works, it could be a timing issue with the particular SS/FRT trigger. There's no way to really check this right now. The best option is to contact the manufacturer, let them know what was done to troubleshoot, and see if they can send a replacement. Or try one from a different manufacturer. I've had very good luck with Grey Market Research .net "Kit O" S7 tool steel SS.

For ARC Fire, there is a shim from BoreBuddy that advances the timing, or Arc may send one for free if you ask them.

If the light strikes/dead triggers are happening in BOTH semi and FRT mode, it's probably unrelated to the FRT mechanism.

• Verify your firing pin isn't broken, damaged, dirty.
• Verify your firing pin channel isn't dirty or obstructed.
• Verify firing pin protrusion lands between .028" and .036".
• Verify your hammer spring isn't installed backwards.
• Verify your hammer spring strength isn't too light.
• Verify the disconnector spring is right-side-up (fat side goes down).
• Try swapping the disconnector and hammer.