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July 23, 2026

HK UMP FRT 2026: GDI-3D Reset-Capable Lower Kit

The one manufacturer-documented forced reset path for the HK UMP45 is GDI-3D's assembled active-reset lower. What the kit includes, which UMP45 and USC45 hosts it fits, the magazine caveat, and where forced reset triggers are legal.

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GDI-3D UMP45 GDI Lower Kit

The sole manufacturer-documented UMP45 active-reset lower path

$700

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HK UMP45Forced resetUMP45 only

HK UMP FRT 2026: GDI-3D Reset-Capable Lower Kit

Q: Which UMP variants does the GDI-3D lower fit?

GDI-3D sells the product as the UMP45 GDI Lower Kit and exposes order selections for Defgunz9/S5 Tactical, Omega Gideon Shadow, Tommy Built, and HK USC45. Its product page does not list UMP9 or UMP40 fitment, so treat this as a UMP45 and USC45-conversion path only and do not extend it to the 9mm or .40 caliber UMP variants.

Q: What comes with the UMP45 GDI Lower Kit?

The standard order includes the UMP45 lower, the lever trip bar, and an installed active-reset device. The optional USC45 stock-block package adds a stock block with an installed buffer, a stock-block axle pin, stock installation hardware, and a double-stack magazine cut jig. A stock is not included, and GDI-3D lists the lower as compatible with factory backing plates and HDPS/HKP stock blocks.

Q: Can the GDI-3D UMP45 lower use an AR-15 forced reset trigger or selector?

The GDI-3D UMP45 lower ships with its own installed active-reset device, and GDI-3D does not publish compatibility with a separate AR-15 forced-reset cassette or forced-reset selector for this platform. The UMP is a blowback subgun, not an AR-pattern host, so do not assume an AR-15 forced-reset device transfers to it. The documented path is the assembled active-reset lower GDI-3D sells.

Q: Does the UMP45 kit require a separate trip kit?

No. GDI-3D lists a lever trip bar and an installed active-reset device as included parts of the assembled lower, with no separate add-on trip kit to buy. The reset hardware ships already fitted in the lower, which is what distinguishes this from the conversion-lower plus trip-kit stacks other non-AR hosts require.

Q: Where are forced reset triggers restricted?

Forced reset triggers are federally legal, and state law is the constraint. As of July 2026 they are banned in California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maryland, Massachusetts, Minnesota, Nevada, New Jersey, New York, Oregon, Rhode Island, and Washington D.C. Florida is restricted because its broad rapid-fire statute is untested as applied to one-pull FRTs. Confirm the current rule for your state before you order.

The HK UMP forced reset path is not a bare cassette you drop into a factory housing. GDI-3D builds a complete UMP45 lower with the reset device already installed, so the reset-capable object you buy is the lower itself, not a part that adapts an AR-15 trigger onto the gun. This guide covers exactly what the GDI-3D kit includes, which UMP45 and USC45 hosts the maker lists, the factory-magazine caveat, why AR-15 forced reset devices do not simply carry over to this blowback subgun, and where forced reset triggers are legal.

By AB|Last reviewed July 2026

Key Takeaways

→One documented path: the GDI-3D UMP45 GDI Lower Kit ($700) is the manufacturer-documented active-reset lower for the UMP45. It ships fully assembled rather than as a loose trigger.
→Everything is installed: the standard order includes the UMP45 lower, the lever trip bar, and the installed active-reset device. There is no separate trip kit to source and time.
→UMP45 and USC45, not UMP9 or UMP40: GDI-3D lists Defgunz9/S5 Tactical, Omega Gideon Shadow, Tommy Built, and HK USC45 selections, and does not list UMP9 or UMP40 fitment.
→Factory magazines only: GDI-3D tested the assembled lower with factory HK UMP magazines and does not guarantee function with aftermarket magazines. Plan the build around factory sticks.
→15 jurisdictions ban FRTs: the mechanism is federally legal, but state law bans it in 15 places and Florida is restricted under an untested statute.

The UMP45 Active-Reset Lower

The UMP forced reset path is a complete lower, and GDI-3D builds it. The GDI-3D UMP45 GDI Lower Kit ($700) ships fully assembled with the UMP45 lower, a lever trip bar, and an installed active-reset device that drives the trigger forward as the action cycles and fires one round per trigger pull. Because the reset device comes installed in the lower, there is no cassette to fit or trip kit to time; the reset-capable hardware is the lower you receive.

That assembled-lower approach is the same conceptual answer used on other non-AR subguns, where the host has no AR fire-control pocket to accept a bare FRT. On the HK MP5 the field runs from complete AR-fire-control lowers to drop-in cassettes, covered in our MP5 forced reset trigger guide, and the closest structural sibling to the UMP is the MAC family, where a dedicated FRT is cut for the host rather than adapted from an AR. The FRT buyer's guide is the category hub across every platform.

UMP45 / USC45 · 45 ACP

GDI-3D UMP45 GDI Lower Kit

A fully assembled active-reset lower built for UMP45-pattern hosts and USC45 conversions. It ships with the UMP45 lower, a lever trip bar, and an installed active-reset device. GDI-3D lists a three-position lever selector, clone selections for Defgunz9/S5 Tactical, Omega Gideon Shadow, Tommy Built, and HK USC45, and an optional USC45 stock-block kit. The maker does not list UMP9 or UMP40 fitment.

Fully assembled UMP45 lower with the lever trip bar installed
Installed active-reset device, no separate cassette to source
Optional USC45 stock-block conversion package
Listed lead time is 6 to 8 weeks

$700.00MSRP

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Forced reset trigger legality is state-specific. Verify federal, state, and local law before purchasing or installing.

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Which Hosts the GDI-3D Lower Fits

UMP45-pattern builds and USC45 conversions, in the specific selections GDI-3D lists. The order page exposes selections for Defgunz9/S5 Tactical, Omega Gideon Shadow, Tommy Built, and HK USC45, so a buyer picks the host at checkout rather than guessing at fitment. The maker does not list UMP9 or UMP40 compatibility, so the 9mm and .40 caliber UMP variants are outside the documented path.

HK UMP45
Documented
What GDI-3D ListsThe pattern the lower is built for, in 45 ACP. Ships fully assembled with the reset device installed.
HK USC45 conversion
Documented
What GDI-3D ListsListed as a selection. The optional stock-block kit consolidates the buffered block, axle pin, stock hardware, and a double-stack magazine cut jig.
Defgunz9/S5 Tactical, Omega Gideon Shadow, Tommy Built
Documented
What GDI-3D ListsNamed clone selections on the order page, so the host is chosen at checkout.
UMP9 / UMP40
Not listed
What GDI-3D ListsGDI-3D does not list 9mm or .40 caliber UMP fitment. Nothing outside the maker's stated selections is verified.

Host	Status	What GDI-3D Lists
HK UMP45	Documented	The pattern the lower is built for, in 45 ACP. Ships fully assembled with the reset device installed.
HK USC45 conversion	Documented	Listed as a selection. The optional stock-block kit consolidates the buffered block, axle pin, stock hardware, and a double-stack magazine cut jig.
Defgunz9/S5 Tactical, Omega Gideon Shadow, Tommy Built	Documented	Named clone selections on the order page, so the host is chosen at checkout.
UMP9 / UMP40	Not listed	GDI-3D does not list 9mm or .40 caliber UMP fitment. Nothing outside the maker's stated selections is verified.

Treat that table as the ceiling. GDI-3D tested the assembled lower with factory HK UMP magazines and does not guarantee function with aftermarket magazines, so a forced reset UMP45 build should standardize on factory sticks rather than gamble on a third-party magazine that may upset the reset timing. GDI-3D also warns that the host bolt must have a functioning firing-pin safety, because some aftermarket bolts without one can discharge out of battery; confirm your bolt before the lower goes in. The USC45 route is the other documented host: the optional stock-block package turns a USC45 into the double-stack UMP configuration with the buffered block, axle pin, stock hardware, and the magazine cut jig in one kit.

Why AR-15 Forced Reset Claims Do Not Carry Over

An AR-15 forced reset trigger is a cassette cut for an AR fire-control pocket, and a forced reset selector replaces an AR-pattern safety selector and rides against the bolt carrier. The UMP is a blowback subgun with neither an AR fire-control pocket nor an AR safety selector, so an AR-15 forced reset device has nowhere to seat on it. GDI-3D's answer is to build the reset into a complete UMP45 lower instead of adapting an AR part, which is why the reset-capable object here is the lower and not a drop-in trigger.

GDI-3D does not publish compatibility between this lower and any separate AR-15 forced-reset cassette or selector; the assembled lower is the documented path. For how forced reset selectors work on the AR-pattern hosts that do take them, see our Super Safety guide. For a worked example of another non-AR subgun that needs host-specific enabling hardware rather than a bare AR device, our SIG MCX forced reset guide and MAC-10 and MAC-11 FRT guide cover the same closed-world logic on their own platforms.

Where a Forced Reset UMP Is Legal

Forced reset triggers are federally legal, and state law is the constraint that matters. The May 2025 DOJ settlement with Rare Breed established that the FRT mechanism fires one round per function of the trigger, so it is not a machine gun under the National Firearms Act and carries no tax stamp and no registration. That settlement covers the trigger mechanism itself; the host firearm's own rules are unchanged, so a UMP45 configured with a stock and a barrel under 16 inches is still a short-barreled rifle that needs its own Form 1 or Form 4 before any trigger goes in.

As of July 2026, forced reset triggers are banned in 15 jurisdictions: California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maryland, Massachusetts, Minnesota, Nevada, New Jersey, New York, Oregon, Rhode Island, and Washington D.C. Florida is restricted because its broad rapid-fire statute has not been tested as applied to one-pull FRTs, and makers routinely decline Florida shipments as a result. A maker's no-ship list is shipping policy, not statute, so check the current rule for your own state before you order rather than reading a checkout screen as a legal ruling. This is the area of firearm law that moves fastest, and the FRT-compatible platform map tracks which hosts have a forced reset path at all.

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HK UMP Forced Reset Trigger FAQ

▶Which UMP variants does the GDI-3D lower fit?

GDI-3D sells the product as the UMP45 GDI Lower Kit and exposes order selections for Defgunz9/S5 Tactical, Omega Gideon Shadow, Tommy Built, and HK USC45. Its product page does not list UMP9 or UMP40 fitment, so treat this as a UMP45 and USC45-conversion path only and do not extend it to the 9mm or .40 caliber UMP variants.

▶What comes with the UMP45 GDI Lower Kit?

The standard order includes the UMP45 lower, the lever trip bar, and an installed active-reset device. The optional USC45 stock-block package adds a stock block with an installed buffer, a stock-block axle pin, stock installation hardware, and a double-stack magazine cut jig. A stock is not included, and GDI-3D lists the lower as compatible with factory backing plates and HDPS/HKP stock blocks.

▶Can the GDI-3D UMP45 lower use an AR-15 forced reset trigger or selector?

The GDI-3D UMP45 lower ships with its own installed active-reset device, and GDI-3D does not publish compatibility with a separate AR-15 forced-reset cassette or forced-reset selector for this platform. The UMP is a blowback subgun, not an AR-pattern host, so do not assume an AR-15 forced-reset device transfers to it. The documented path is the assembled active-reset lower GDI-3D sells.

▶Does the UMP45 kit require a separate trip kit?

No. GDI-3D lists a lever trip bar and an installed active-reset device as included parts of the assembled lower, with no separate add-on trip kit to buy. The reset hardware ships already fitted in the lower, which is what distinguishes this from the conversion-lower plus trip-kit stacks other non-AR hosts require.

▶Where are forced reset triggers restricted?

Forced reset triggers are federally legal, and state law is the constraint. As of July 2026 they are banned in California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maryland, Massachusetts, Minnesota, Nevada, New Jersey, New York, Oregon, Rhode Island, and Washington D.C. Florida is restricted because its broad rapid-fire statute is untested as applied to one-pull FRTs. Confirm the current rule for your state before you order.

ABAuthor

Avid shooter with 10+ years of experience including competition shooting, and an associate member of the Professional Outdoor Media Association (POMA). Built 10+ AR-pattern rifles and several handgun platforms for home defense, competition, and suppressed night shooting.

10+ years shooting experienceCompetition shooterBuilt 10+ AR-pattern riflesAssociate member of the Professional Outdoor Media Association (POMA)

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