Binary trigger for the AR-15 with Safe, Semi and Echo modes. No longer stocked at Western Sport — see our forced reset selectors for a faster AR-15 trigger setup that ships to your door.
The Fostech Echo AR-II Trigger (often searched as the Fostech Echo 2) is a drop-in binary trigger for the AR-15 with three modes: Safe, Semi and Echo. In Echo mode it fires one round when you pull the trigger and a second when you release it, so you get two shots per pull-and-release without converting the rifle to full auto and without NFA paperwork. Made in the USA by Fostech, it ships to your door with no FFL.
What it is: a binary (“echo”) trigger for the AR-15: one shot on the pull, one on the release in Echo mode.
Modes: Safe (will not fire), Semi (fires on the pull), Echo (fires on the pull and on the release).
Platform: AR-15 only, per Fostech. Not for AR-10s.
What your rifle needs: a full-auto (M16-cut) bolt carrier, a mil-spec lower with standard trigger pins and no sear block, and a standard carbine or rifle buffer (Fostech recommends an H or H2).
Not compatible with: lowers with a sear block or extra sear wall, large-pin lowers, most carbon fiber or polymer lowers with extra supports, and solid, sand-filled or captured-spring buffers.
Availability: no longer stocked at Western Sport; this page stays up as a reference.
How the Echo AR-II works
In Semi, the Echo AR-II behaves like a normal single-stage AR-15 trigger: one round per pull. Switch to Echo and the trigger releases the hammer twice, once when you pull and once when you let the trigger travel forward. You control the second shot with your release, so the rate is set by your finger, not by the gas system. If you are in Echo mode with the trigger held back and decide not to fire the release shot, moving the selector to Safe before releasing prevents it.
A binary trigger is a different mechanism from a forced reset trigger. An FRT fires once per pull and forces the trigger to reset quickly; a binary fires on both the pull and the release. If you are deciding between the two, see how forced reset triggers work and our forced reset trigger category.
Specifications
Manufacturer
Fostech
Model
Echo AR-II
Manufacturer part number
4150
UPC
639266300021
Type
Binary (echo) trigger with ambidextrous selector
Modes
Safe / Semi / Echo
Platform
AR-15 only
Origin
Made in the USA
Included (per Fostech’s manual): the Echo assembly, trigger body and hammer, selector cam, short and long selector levers with screw, and the small parts needed to install them. Not included: bolt carrier group, safety detent and spring, trigger pins and pistol grip.
Mil-spec AR-15 lower with standard trigger pins (anti-walk pins are fine). No sear block, extra sear wall or set screws in the way of the trigger.
Buffer
A matching carbine or rifle buffer assembly, H or H2 recommended. Not solid, sand-filled or captured-spring buffers. See buffers and buffer tube kits.
Tools
3/32″ Allen wrench and gun grease, per Fostech’s manual
What to know before you buy
There is a learning curve. The second shot comes when you release the trigger, so your first magazine in Echo mode will feel different. Start with a few rounds and let the habit build.
Check fit first. Fostech’s own policy on Echo triggers is that all sales are final, so confirm your carrier, lower and buffer before you order. Our terms are on our return policy page.
State law varies. Binary triggers are sold without NFA paperwork federally, but several states and cities restrict them.
This item ships to most U.S. states. State and local laws on forced-reset and rapid-fire devices vary and continue to change, so we do not ship this product to any state or jurisdiction where its legality is restricted, disputed, or dependent on the carrier. The list below is deliberately conservative: if there is meaningful risk, we do not ship there.
States and jurisdictions we do not ship to
California
Colorado
Connecticut
Delaware
District of Columbia
Florida
Hawaii
Illinois
Iowa
Maryland
Massachusetts
Minnesota
Nevada
New Jersey
New York
Oregon
Rhode Island
Virginia
Washington
U.S. territories
International destinations
Florida and Minnesota restrict retail sales of these devices, and shipments into Iowa and Virginia depend on carrier and distributor policy rather than on a settled rule. We treat all four as no-ship states. Municipal bans such as Chicago, Illinois and Denver, Colorado sit inside states already on the list above.
State statutes and retail shipping policies change frequently. Always verify current local legislation and consult legal counsel prior to shipping. If you are not sure whether we can ship to your address, send us a message before you order and we will tell you before we take your money.
Fostech Echo AR-II FAQ
Is the Fostech Echo AR-II trigger legal?
Federally, binary triggers like the Echo AR-II are sold as ordinary parts with no NFA paperwork, because each round follows a separate function of the trigger: one on the pull and one on the release. Several states and cities restrict binary triggers, so check where you live before ordering. This is not legal advice.
What is an echo trigger?
An echo trigger is Fostech’s name for its binary trigger. In Echo mode the rifle fires once when you pull the trigger and again when you release it.
Does the Fostech Echo need a full-auto bolt carrier?
Yes. Fostech says you need a full-auto (M16-cut) bolt carrier for the Echo AR-II to function.
Does the Echo AR-II fit an AR-10?
No. Fostech designed the Echo AR-II for the AR-15 platform only.
What are common problems with the Fostech Echo 2?
Most problems trace back to the rifle rather than the trigger: a semi-auto bolt carrier instead of an M16-cut carrier, a lower with a sear block or large pins, or a solid, sand-filled or captured-spring buffer. Fostech recommends a standard H or H2 buffer.
How is a binary trigger different from a forced reset trigger?
A binary trigger fires on both the pull and the release. A forced reset trigger fires only on the pull, but uses the bolt carrier to force the trigger forward to reset almost instantly. Both fire one round per function of the trigger.
What if the Echo AR-II does not work in my rifle?
Fostech’s own policy on Echo triggers is that all sales are final, so please confirm your bolt carrier, lower and buffer before ordering, and see our return policy. Send us a message if you want help checking your rifle first.
Specifications and requirements from Fostech. Western Sport is a retailer, not the manufacturer.
Additional information
Weight
2 lbs
Dimensions
11 × 13 × 2 in
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This item is out of stock. These are on the shelf today and ship or transfer the same way. Not sure which is the right swap? Call 817-393-4000 and we will tell you straight.
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