AS Designs HK416/MR556 ARC-Fire Trigger 3-Position Ambi Controls

HK416, MR556 3-Position ARC-Fire Trigger with Ambidextrous Controls

AS Designs' ARC-Fire (Active Reset Clutch) trigger is a forced reset-style trigger that resets immediately after each shot for rapid follow-up shots (one compliant round per trigger action).

Platform compatibility

• Direct fit in MR556 and HK416 firearms (ambi selector levers do not align with the factory pictogram; see included pics).
• Only the included selector levers are compatible with the ARC-Fire kit because the selector lever is part of the ARC mechanism.
• Does not require a full-auto BCG, but a FA BCG may keep the trip lever from flipping backwards and disengaging.
• If using a semi-auto BCG: actuating the charging handle with the muzzle pointed up disengages the trip lever; point the muzzle toward the ground and actuate again to reposition the trip lever.

Compatible with

• HK416 A5 (1.8mm gas vent screw recommended)
• HK MR556 A4 (1.8mm gas vent screw recommended)
• HK MR556 A1 (requires an adjustable gas block to cycle)
• HK416 A1, A3 (requires an adjustable gas block to cycle)

Gas vent screw guidance

• MR556 A4 rifles and pistols are factory-equipped with a 1.3mm gas vent screw.
• 1.8mm was optimal for an MR556 A4 using 11" and 16" barrel rifles with standard M195 ball 55gr 5.56.
• Most configurations cycle well with a gas vent screw in the 1.6mm–2.0mm range.

Ejection guidance

• Expected ejection pattern: approximately 3–4 o'clock.
• Closer to 1 o'clock (over-gassed): go UP in vent screw size (CLOSE gas block).
• Closer to 5 o'clock (under-gassed): go DOWN in vent screw size (OPEN gas block).

Restricted states

CA, CT, DE, FL, HI, IL, MA, MD, MN, NJ, NV, NY, OR, RI, VA, WA, DC

No US Territories or international orders.