I suspect you will need to eat your hat.
The bottom of the Fostech bolt is visible at the end of Tim's videos (MAC). It clearly shows a chamfer at the location where it would contact an auto sear. The Fostech part is different from a conventional auto sear in that it has a tail/extra material. (see your picture above) I suspect that this chamfer and tail prevent a standard auto bolt carrier group from fully seating and operating properly. It is unclear if there are other differences, but the presence of this chamfer makes the Fostech bolt proprietary.
It makes sense! ! Then they can sell the trigger packs cheaper to compete with the Franklin Binary .
I just ordered a echo gen 2 hopefully its not too hard to install
You might think that but they didn't lower the price.
What do they sell for ?
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My Gen II Echo trigger works great on my AR .223
Next time out I intend to put my 7.62x39 AR upper on the lower that has the Echo trigger.
My only concern is if the hammer spring is strong enough on the Echo trigger to ignite those Russian steel case primers.
I had to add a Wolff extra power hammer spring in my X39 AR to get reliable ignition with Russian steel case ammo.
If that works I may consider putting the Echo trigger in my CMMG Mutant and mag dump a 75 rd AK drum mag LOL
Just sharing a Fostech AR trigger reassembly experience:
Short story: I found out the hard way via google fu: Guide rods (2 black thingies with spring around them) the u shaped ends are supposed to be flat side facing outward.