First off I am a SIG MPX fanboi.
There is much to like about them; piston operation stays clean, the ability to use folding or collapsing stock, solid construction, and they are more fun to shoot than I can describe. I put a red dot on mine and it will run anything I put in it. Well, as long as the length is correct. My mouse-fart production loads run very smoothly and I can hit 50 yard steel off hand with no issues and 100 and 200 are easy off a rest.
When I bought it I switched out the trigger. It is the worse monstrosity I have come a cross in a firearm. Even M16’s fresh from rebuild were better than the MPX trigger.
I’ve had two mechanical failures. The first was minor. A roll pin in the charging handle broke. The locking lever on one side came off. I bought a replacement locally and I was back in action.
But today it was different. Running the carbine and it stopped going bang. Slap, rack and click. Dammit. Repeat. Dammit. After five round I give up. All five round show no sign of a primer strike.
When I got home I took it apart. The firing pin broke. But it’s okay because the tip lodged in the firing pin hole in the bolt.
Tomorrow I call SIG about a replacement firing pin. An internet search shows that this is not an uncommon problem in early Gen 2 carbines.