Posted by Myth Industries on Apr 26th 2026

FRT Trigger in a AR9 (9mm): An Installation Guide

Installing a Forced Reset Trigger (FRT) in an AR9 (9mm AR pistol/carbine) is doable and popular for faster semi-auto fire, but it requires specific parts and tuning because AR9s are blowback-operated (no gas system) with a heavier, often one-piece or weighted BCG.

Standard AR-15 FRTs (Super Safety, Super Selektor/Atrius, Partisan Disruptor, Rare Breed FRT-15L3, etc.) work in most AR-15 pattern AR9 lowers, but the BCG interaction, recoil management, and feeding become critical at the elevated cyclic rates.

Core Requirements

  • Compatible FRT system: Most selector-style (Super Safety/Selektor) or cassette-style (Partisan Disruptor, Rare Breed) FRTs install like in a 5.56 AR but need AR9-specific tuning. Some kits include a pre-cut trigger for Super Safety compatibility.
  • M16/full-auto profile BCG compatibility (or equivalent trip surface on the 9mm carrier).
  • Heavy recoil management (buffer + spring).
  • Reliable feeding setup (barrel + ammo).

Cut Bolt Carrier Group (Essential for Most Setups)

The 9mm BCG (typically Colt/Glock pattern blowback) has a rear bolt weight or carrier extension that often interferes with the FRT’s reset cam/lever or fails to properly trip the forced reset mechanism.

What “cut BCG” means:

  • Remove the rear bolt weight entirely (common first step).
  • Notch/file/Dremel a step or clearance cut on the weight (or carrier rear) so the FRT trip surface/lever has clear space (~0.63″ height from top of bolt to bottom of notch; remove ~3.5mm+ from the bottom of the weight).
  • This allows the recoiling carrier to fully engage the reset cam without binding and ensures the bolt trips the mechanism properly for forced reset.
  • Some BCGs (e.g., certain Foxtrot Mike, IDL Gen 3, or KAK with extra-heavy tungsten weights) need minimal or no cut if the weight sits back far enough.

Why it’s needed: Without the cut, the lever can prevent full bolt closure or the reset won’t engage reliably, causing malfunctions or no forced reset.

Tools for cut: Dremel, belt sander, or mill (easy on removable weights). Test fit with upper off.

Kynshot RB5007 Hydraulic Buffer (Highly Recommended)

This stainless steel hydraulic buffer (5.9 oz, carbine-tube length) is specifically engineered for 9mm AR9 PCCs (3.5–7.5″ barrels).

Why it pairs excellently with FRT:

  • Absorbs rearward energy, drastically reduces bolt bounce and felt recoil.
  • Smooths the faster cycling from forced reset (prevents light primer strikes, out-of-battery issues).
  • Users report it makes FRT-15L3 or similar “run like a raped ape” in PSA/H&R AR9s.
  • Works in standard carbine buffer tubes (or A5 with spacer if needed). Pair with a standard or AR10-length spring for best results.

It’s often the “missing piece” for reliable FRT function in blowback 9mm where a standard H2/H3 buffer alone may be too light or bouncy.

9mm Barrel with Feed Ramp

This is not an FRT-specific requirement but is strongly advised for overall reliability—especially with FRT’s higher rate of fire.

Why it matters:

  • Standard AR9 barrels can have feeding issues with hollow points or defensive ammo.
  • Enhanced feed ramp/cone (e.g., Brigade BM-9 V3, TACCOM Super Feed, or reprofiled barrels) creates a smooth “funnel” for reliable chambering.
  • FRT doesn’t change barrel function, but faster follow-ups increase the chance of stoppages if feeding is marginal. A good ramped barrel ensures consistent performance without bolt bounce or light strikes.

Other Items Typically Needed

  • Buffer spring: Often a heavier AR10-style or extra-power spring (some Super Safety installs specify this with 10+ oz buffers).
  • Anti-walk/anti-rotation trigger & hammer pins (recommended for any FRT).
  • 3-position selector (included with Partisan/Atrius; required for Super Safety kits).
  • Total reciprocating mass tuning: Aim for ~21–24 oz combined BCG + buffer weight for smooth FRT operation in 9mm blowback.

General Installation Overview

  1. Modify BCG first — Cut/notch the rear weight as described.
  2. Install FRT — Drop-in style (Partisan/Rare Breed) or selector swap (Super Safety/Selektor) follows standard AR lower procedures. Clear firearm, remove grip/safety/old trigger group, install new parts.
  3. Install Kynshot RB5007 + spring — Drop into buffer tube.
  4. Reassemble and function test — Dry fire in all modes (safe/semi/super). Manually cycle BCG to confirm reset and no binding. Check barrel feeding with dummy rounds.
  5. Live fire incrementally — Start with single shots, then controlled pairs. Tune if needed (buffer weight, cut depth).

Follow your specific FRT manufacturer’s guide for AR9 tweaks.

Safety & Legal Notes: This is a performance modification. Improper BCG cut or tuning can cause malfunctions. Always function test thoroughly and follow all firearm safety rules. FRTs are semi-automatic but face state restrictions (e.g., banned in CA, NY, etc.). Verify legality where you live. Consult a qualified gunsmith if unsure.

With a properly cut BCG, Kynshot RB5007, and feed-ramped barrel, most AR9 builds run FRTs extremely well—fast, reliable, and fun.