I've broken three Rock River Match hammers. All occurred at around the three thousand round mark --- Only the incidents occurred while using a 22 long rifle dedicated upper. Rock River replaced the trigger groups for free. But I later switched to a mil-spec hammer --- Though I have mothballed my two dedicated 22 uppers...due to the danger of OOB's occurring. The OOB's happened three times for me...though fortunately, no one was hurt. Appleseed has banned the use of 22 lr S&W M&P 15's in their competitions, some years ago, due to the danger of OOB's occurring. Though the dedicated 22 uppers I used were not Smith & Wesson.

I believe it was Clint Smith...of Thunder Ranch Training Academy, who insisted that anyone going to train at Gunsite...only use a mil-spec hammer in their AR's --- due to evidence of match grade hammers breaking during training. He also advised them to bring an extra mil spec hammer and other assorted AR parts.

I have never used a KAC hammer in any of my AR's...but I'll check into it --- Thanks