I just got the 5.45x39 NiB M16 Bolt Carrier Group from aim surplus a week ago. Memorial day weekend was the first weekend i had the chance to try it out.

Everything loaded fine. But when i pulled the trigger, all i got was a "click", no "BOOOM!!". I am using surplus ammo. And i have a S&W upper with the heavy spring in the lower.

I would eject the round out, and it would have a decent sized dimple in it like you would find in fired brass. I would load that same round back in and fire it again and it would actually fire the round on the second hit.

I didnt bring my old BCG with me to swap out, i didnt think there would be an issue with any spikes stuff.

I can only think of two possibilities.

1. Firing pin out of spec.
2. I used a fail Zero hammer with the 5.45x39 NiB M16 Bolt Carrier Group, maybe an issue with the hammer some how?

I live in suburbia. So it will be a while before i get a chance to try it out again. I might just pull some of the bullets on my reloading press and dump the powder and just try different things in my garage and see if i can get the primers to ignite.

Does any one else have any ideas? This is a first for me with any AR platform. Ive never had an issue with a BCG like this. Typicaly i would say to some one else that you forgot to put in the heavy spring, but its in there. But its acting like it doesnt have the heavy spring. So i dont know.... I need some shared wisdom on this one.

Got it figured out i think. I put the original hammer back in, and I pulled a bullet and just fired the primer. Everything worked just fine. I only tried one round. But i couldnt get a single one to work saturday.

So hopefully everything is fixed. I dont understand why the Fail Zero hammer didnt work.

Sounds like a weak hammer spring. Even surplus ammo sellers recommend a firm hammer spring when firing surplus 5.45 ammo.