Vital information for ar-9 users - Fostech Echo AR-II Drop-In Binary AR-15 Trigger

Built my first AR myself and decided to do an AR9. Did my due diligence and read up as much as I could find on setup. Picked this trigger to make the gun more fun and bec 9mm ammo is the cheapest. I did not read ANYWHERE anything about bcg specifics except that you can run a standard AR bcg now with this newer version of the echo trigger (original version required use of their bcg). That’s true, if you are running a standard AR-15 bcg. Not if you are running an AR-9 bcg as they are slightly different. Took my completed AR-9 to the range and it ran 100% in semi auto mode and about 60% reliably in “ECHO” mode. Figured I had made an error with something in the build so I called FOSTECH and spoke with their spectacular customer service person (AMY) who said that I would either need to modify my AR-9 bcg to make room for the trigger lock mechanism or I could buy their pre-modified AR-9 bcg for $155. Not saying anything negative about the price because if I hadn’t already bought one, I would have been thrilled to buy theirs knowing it was going to work perfectly in harmony with their trigger. However, FOSTECH does not list those bcg’s on their website and I didn’t find any information anywhere about this requirement regarding AR-9 bcgs. So be forewarned and informed, the AR-9 build requires a special FOSTECH bcg or to modify your own to make a notch cut out for the trigger lock on the ECHO II AR trigger. I plan to take mine to a friend who has a machine shop and make the adjustment. I completely believe that this trigger will go from running 60% reliably in my imperfect build to 100% reliably once I modify the bcg correctly.

Just wanted to put this info out there as there are so many variables with the AR-9 build and when it doesn’t run correctly, you can spend a lot of time and money trying to figure it out. That’s the path I was about to venture out on but luckily I was able to get this info straight from FOSTECH about how to make this trigger run correctly.

Install was initially overwhelming but once I just followed the directions and took my time, it was fine. More challenging than a normal drop in trigger but not something that requires any special skills. I will admit I blew mine apart exactly the way they say NOT to do and had some pieces and parts fly off it like a transformer...but the video link they provide if you make that mistake is very good so don’t sweat it.

FOSTECH did also say that in addition to the bcg mod, it is essential that you run a H or H2 buffer to get adequate “dwell” time. FYI