Knight’s Armament Company/Stoner has primarily been a defense contractor making weapons and SOPMOD weapons packages for USSOCOM. Only in recent years have they started a commercial division, KMC, to market stuff for civilians. On their SR16 Stoner rifle, they make a parallel SR15, Stoner was tasked with improving his original bolt design to either reduce or eliminate some of the common failures and breakages experienced by the military:
1. His original square lug design would develop cracks at the base, which would result in broken lugs. He corrected this by using a new rounded lug design, having web reinforcement at the lug base. Results, cracks no longer develop and lugs do not break.
2. His original design extractor tended to lift due to bolt rotational forces on fast cycles. He corrected this by re-designing the extractor, it is now T-shaped, using two coil springs, and he change the pin location to improve angles. Results, the lifting issue was eliminated.
3. His original design cam pin would develop cracks at its location on the bolt, and the bolt would break. He corrected this by re-designing the cam pin so that this area could be beefed up. Results, cracks no longer develop and the bolt does not break.
4. His original design would capture debris along the bolt face. He corrected this by adding a debris groove. Result, this is no longer an issue.
Stoner’s improvements over his old design was dubbed the E3 bolt. I run this bolt in my Mod2. The twin sister to my KAC is now in a museum. It was torture tested for a year, without cleaning, and without maintenance. It went over 20,0000 rounds without fail, and in the end, it still passed testing and held under moa. A couple of the military guys who are now instructors, ran maintained E3 bolts, and were seeing 60-70,000 rounds before cycling them out. Not just a strong testament for the E3, but for the entire KAC Stoner rifle. I do not believe there is a documented incident of an E3 bolt breakage.
You cannot run a round lug E-3 bolt in a square lug Colt. But, if needed for an emergency battlefield repair, you can run a mil-spec square lug bolt in a KAC, and it will function. But it is for an emergency field repair, not a long term repair, as the square lug would cause excessive wear and damage.
Very, very, few people are in the position to run their rifle long and hard enough to appreciate the enhancements that KAC brings to the table. For most, you would do fine with a standard mil-spec bolt, and just replace or fix it as it breaks down. But as for Colt, or anybody, vs KAC, KAC has some proprietary parts that are markedly superior to what anyone else can bring to the table. It is my favorite, by far, for an out the box gun.
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