Roller-delayed · SEF trigger groups · HK pattern [email protected]
Trigger groups & spares
Shipped from the USA In stock now
FRT-RD3™ (SEF) Two-Stage (3-Position) Forced Reset Trigger for the HK MP5, MP5K, SP5 & SP5K
Fig. 1FRT-RD3Host: MP5 · MP5K · SP5 · SP5K
RD3 · SEF housing · MP5 pattern

The roller-delayed parts counter

This counter is built around one family of guns: the roller-delayed HK pattern. The RD3 triggers and SEF selector parts are the core of it, the HK 5.56 and B&T units sit beside them, and the AR-15 and AK lines are here because most people who own an MP5 own one of those as well. Every reference listed is on the shelf.

HostMP5 · MP5K · SP5 · SP5K
GroupSEF housing, two-stage
PositionsS / E — safe and single fire
FittingDrop-in, no machining
Dispatch1–2 business days, tracked
$462.72In Stock
Free US shipping · leaves the bench in 1–2 business days
Open the data sheet The counter
Maker-sourced partsSecure checkoutCard or crypto
MP5 FRT is an independent retailer. Rare Breed Triggers, Heckler & Koch, B&T, PTR and every other name on this site belong to their owners and are used to say what a part fits, nothing more.

Two positions, and that is the whole range

S E SEF HOUSING
S — safe

Selector back and the trigger is dead. Nothing in the housing can move, and that is how the gun travels and how it sits in the safe.

E — single fire

One round for every separate pull of the trigger, exactly like the group it replaces. The carrier returns the trigger to the reset point; your finger still fires the shot.

A military SEF housing carries a third mark. Nothing sold here has one, and nothing sold here can be made to have one. Semi-automatic components only, no machine guns and no conversion devices of any kind.

On the counter

This counter is built around one family of guns: the roller-delayed HK pattern. The RD3 triggers and SEF selector parts are the core of it, the HK 5.56 and B&T units sit beside them, and the AR-15 and AK lines are here because most people who own an MP5 own one of those as well. Every reference listed is on the shelf.

MP5 & HK triggers 6Forced reset triggers 19Selectors & parts 22AR-15 parts & buffers 10Magazines 2Tools & install kits 2
Rare Breed Triggers FRT-RD3™ (SEF) 3-Position Selector
MP5 · MP5K · SP5 · SP5K
Rare Breed Triggers FRT-RD3™ (SEF) 3-Position Selector
Contents: 1 x RD3 SEF Single-Sided Safety Selector 1 x 1/16″ Allen Key 1 x 3/32″ Allen Key
$95.00
Details
FRT-RD3™ (AMBI) Two-Stage (3-Position) Forced Reset Trigger for the HK MP5, MP5K, SP5 & SP5K
MP5 · MP5K · SP5 · SP5K
FRT-RD3™ (AMBI) Two-Stage (3-Position) Forced Reset Trigger for the HK MP5, MP5K, SP5 &
Drop-in forced reset trigger for the HK MP5, MP5K, SP5 and SP5K. FRT-RD3 provides a two-stage trigger with a forced reset mechanis
$462.60
Details
3-Position Ambidextrous Selector for the FRT-RD3 (AMBI)
MP5 · MP5K · SP5 · SP5K
3-Position Ambidextrous Selector for the FRT-RD3 (AMBI)
Fits the FRT-RD3 trigger system in roller-delayed HK pattern guns like the MP5 and SP5, offering ambidextrous fire control in a du
$100.00
Details
Screw for the Right Side Ambidextrous Selector Lever for the FRT-RD3 (AMBI)
MP5 · MP5K · SP5 · SP5K
Screw for the Right Side Ambidextrous Selector Lever for the FRT-RD3 (AMBI)
Compatible with the FRT-RD3 trigger, this screw securely attaches the right-side ambidextrous selector lever, ensuring reliable op
$100.00
Details
3-Position SEF Selector for the FRT-RD3 (SEF) – For use with the PTR MP5 Clone
MP5 · MP5K · SP5 · SP5K
3-Position SEF Selector for the FRT-RD3 (SEF) – For use with the PTR MP5 Clone
Fits PTR MP5 clones and works with Rare Breed Triggers' FRT-RD3 system. This 3-position SEF selector offers safe, semi, and full-a
$95.00
Details
FRT-RD3 Safety Detent Kit
MP5 · MP5K · SP5 · SP5K
FRT-RD3 Safety Detent Kit
The FRT-RD3 Safety Detent Kit fits Rare Breed Triggers, replacing worn detents to ensure consistent sear alignment for reliable se
$100.00
Details
FRT-RD3 Tapered Screw Kit for the Right-Side AMBI Selector Lever
MP5 · MP5K · SP5 · SP5K
FRT-RD3 Tapered Screw Kit for the Right-Side AMBI Selector Lever
Fits the Rare Breed Triggers FRT-RD3 right-side Ambi selector lever. This alloy steel tapered screw kit provides a direct replacem
$10.00
Details
FRT-RD3 Selector Detent Kit
MP5 · MP5K · SP5 · SP5K
FRT-RD3 Selector Detent Kit
The FRT-RD3 Selector Detent Kit fits the Rare Breed Triggers FRT-RD3. It includes replacement alloy steel detent components with a
$11.00
Details
FRT-RD3 SEF Selector Kit
MP5 · MP5K · SP5 · SP5K
FRT-RD3 SEF Selector Kit
The FRT-RD3 SEF Selector Kit fits HK pattern guns with SEF grips, featuring a heat-treated 4140 steel selector barrel and anodized
$95.00
Details
FRT-RD3 SEF Selector Kit for the PTR
MP5 · MP5K · SP5 · SP5K
FRT-RD3 SEF Selector Kit for the PTR
Designed for PTR MP5 clones, the FRT-RD3 SEF Selector Kit allows reliable engagement with Rare Breed Triggers' FRT-RD3. Made in th
$95.00
Details

See every part on the counter

Why a roller-delayed gun is fussy about its trigger

TRUNNION ROLLERS BOLT HEAD LOCKING PIECE CARRIER REARWARD TRAVEL

There is no gas system and no buffer to tune on an MP5. The bolt head carries two rollers that sit in recesses in the trunnion. A wedge behind them, the locking piece, holds them out until chamber pressure drives the carrier back hard enough to cam them in. Only then does the whole bolt travel.

That delay is fixed by geometry. It does not drift with gas port size or buffer weight, which is why an RD3 trigger behaves the same on Monday as it does after a thousand rounds, provided the locking piece and recoil spring are healthy.

It also means the fire control group is a separate world from the AR. The MP5 pack is a self-contained housing: the trigger, the selector and the detents all live in it together, so a worn detent shows up as a selector that will not index rather than a trigger that feels wrong.

The practical version: buy the trigger that matches your housing, keep the small parts on the shelf, and replace a spring the first time the reset feels different rather than the tenth time.

Fitment index

Which family of part goes with which host. The AR, AK and HK units are not interchangeable, so start here before you pick a trigger.

HostTrigger familyWhere to look
MP5 · MP5K · SP5 · SP5KFRT-RD3 (SEF or AMBI)MP5 & HK shelf
PTR MP5 clonesFRT-RD3 with the PTR selector kitPTR selector kit
HK MR223 · MR556FRT-MR3 (curved, flat or MIL shoe)FRT-MR3
B&T APC9 · APC45FRT-AP3FRT-AP3
B&T SPC9 · SPC45 · GHMFRT-SG3FRT-SG3
AR-15FRT-15L3 · FRT-15C3 and other AR drop-insAR parts shelf
AK pattern · 7.62×39Diablo AK trigger, SKS unit, transfer platesDiablo AK

FRT guides & resources

MP5 forced reset triggersWhich forced reset trigger fits an HK MP5, MP5K, SP5 or SP5K, how ambi and SEF housings differ, and what to check before

All FRT guides →

Frequently asked questions

Which trigger fits an MP5 or SP5?

The RD3 units. They come in two housings: SEF, with the selector on the left side only, and AMBI, with a selector on both sides. Both fit the MP5, MP5K, SP5 and SP5K. An AR forced reset trigger will not fit any of them.

Is a forced reset trigger a machine gun part?

No. Every part sold here fires one round per separate pull of the trigger. We do not sell machine guns, auto sears, switches or any other conversion device. The legal position on forced reset triggers has moved more than once, and state law varies, so check the current rules where you live before ordering.

SEF or AMBI?

If you shoot from both shoulders, or run the gun with your support hand well forward, the AMBI housing saves you moving your firing hand to work the selector. If you shoot right handed and want the classic layout, take the SEF. The trigger itself is the same.

Do I need a gunsmith?

The RD3 and MR3 units are drop-in and need no machining, but they are still fire control parts in a pack most people have never opened. If you have not stripped the housing before, have a gunsmith fit it and function check the gun.

How fast do orders ship?

Orders placed on a business day leave in one to two working days, tracked, from inside the United States. If a fitment question is holding you up, email before you order and we will confirm the part against your host.