Roller-Delayed and Pistol-Calibre FRTs: MP5, SP5 and PS90

Almost every guide to forced reset hardware is written for the AR-15, which is little help to anyone with an MP5 clone, an SP5 or a PS90. These platforms need purpose-built modules for architectural rather than commercial reasons.

Why an AR trigger will not fit

An AR-15 fire control group sits in a standardised pocket with standardised pin spacing. Roller-delayed HK designs do not share that geometry: the trigger lives in a removable housing with its own pin locations, its own selector interface and a fundamentally different disconnector arrangement. The FN PS90 is further removed still, being a bullpup with a top-loading magazine and a long linkage running back from the trigger to the sear.

A forced reset trigger for these hosts is therefore a separate design, not an adapted AR part. It also means the AR-side selector kits do not cross over — an arc fire frt kit is engineered around an AR-15 disconnector and has no application on a roller-delayed host regardless of how similar the marketing looks. The same caution applies to anything sold under a super safety ar15 heading: the name describes a design pattern, not universal fitment.

MP5, MP5K, SP5 and SP5K

The mainstream option is the FRT-RD3, a three-position cassette built for HK roller-delayed pistols and rifles in SEF and ambidextrous configurations. Searching for an mp5 frt will mostly return this family, and it has the longest track record on the platform.

Two things to confirm before ordering. Grip frame type first: the ambidextrous version requires an ambi grip frame and will not work on a SEF frame. Clone compatibility second — the HK-pattern clone market is large and tolerances vary, so a trigger that drops into a genuine SP5 may need attention in a lower-cost clone.

A budget path exists as well. Three-position units and selector-based kits sit well below cassette prices, and for anyone wanting ambidextrous selector geometry specifically, the atrius super selektor trigger compatibility list is worth checking against the existing trigger first.

Suppressed and SD hosts

Integrally suppressed variants change the pressure curve significantly, which changes carrier timing, which changes reset behaviour. An frt-15l3 trigger tuned for an unsuppressed rifle is no guide to what an SD host will do. Expect to spend time on it, and expect that a unit running perfectly in a standard MP5 may want a different spring set behind a suppressor.

The FN PS90

The PS90 gets one credible option: the Dorin Technologies X-PRT 90, originally sold as the FRT90. It is a drop-in cross progressive reset module engineered around the PS90 linkage, and no AR-pattern substitute exists — a standard FRT-15 will not physically fit under any circumstances.

Two caveats apply. The module fits the PS90 in standard configuration; P90 closed-bolt variants and SBR configurations with non-standard barrel lengths are not covered, and aftermarket fire-control components in the host should be declared before ordering.

Pistol-calibre and rimfire

Outside the HK family the options thin quickly. The Taurus TX22 has the Freedom Finger 22TY, a stainless drop-in module, and the freedom finger frt trigger is close to the only rimfire forced reset product with a real production history. Gen 4 Glock frames have the A.R.T. kit working off slide travel, which is the route to a forced reset trigger for glock and fits Gen 4 only.

For anything else — CZ Scorpion, Kriss Vector, heavily modified clones — assume nothing exists until confirmed, and contact the dealer before ordering rather than after.

What carries across

Less than most people hope. The buffer-and-carrier logic governing AR-15 reliability does not apply to a roller-delayed gun, which has no buffer tube in the AR sense, and does not apply to a bullpup at all. What does carry across is the principle: these devices take their energy from the action cycling, so anything changing the cycling will change how the trigger behaves.

Three-position selectors carry across too. Anyone wanting the option of conventional operation should look for it explicitly; a delta team tactical frt 3 position configuration and an ak super safety 3 position kit both offer it on their respective platforms, and the HK cassettes ship in three-position form as standard.

Information only — not legal advice. Forced reset triggers are lawful under federal law following the May 2025 Department of Justice settlement, but fifteen states and the District of Columbia prohibit them outright and Florida and Virginia are legally contested. Verify the law in your state before purchasing or possessing any rate-of-fire device.