Rare Breed FRT-MR3

The FRT-MR3 is Rare Breed's forced reset trigger for HK's MR-series rifles, and it exists because the MR556 and MR223 do not take a standard AR-15 fire control group cassette without compromise. It is a single-stage, three-position drop-in unit: Safe, Semi, and forced reset. The bolt carrier's rearward travel forces the trigger back into reset after each shot and holds it there until the action returns to battery, so each round still requires an individual press.

The selector is ambidextrous and includes a 45-degree position that matches the MR platform's own selector markings, which is the detail that separates this from a generic FRT dropped into an HK lower. Rare Breed builds it from 7075 anodized aluminum with heat-treated 4140 and S7 steel internals, and the assembled unit weighs 5 oz. The kit ships with two anti-walk pins and four screws, both A1 and A4 selector drums, two selector lever roll pins, and two T10 Torx wrenches, so nothing else needs sourcing for the install.

The hard requirement is the bolt carrier. The MR3 works with the factory semi-automatic MR-series carrier only; HK416 and BRN4 full-auto carriers will not run it. Both blade shapes cost $525 direct, curved or flat, with a two-per-transaction cap. Rare Breed does not ship to CA, CT, DE, HI, IL, MA, MD, NJ, NY, OR, RI, WA, or DC.