Reproduction GX-607 and XM-177 Moderators: Do They Work?

Published on February 6, 2026
Duration: 12:46

This video from Forgotten Weapons, featuring expert Ian McCollum, delves into the functionality and historical context of reproduction XM-177 and GX-607 moderators by Liemohn Mfg. It examines their effectiveness in reducing sound and flash compared to original designs and dummy suppressors, referencing 1968 test data and the ATF's 1975 ruling on their classification as suppressors. The discussion highlights the historical need for such devices in Vietnam and their technical specifications, durability, and legal implications.

Quick Summary

Expert Ian McCollum of Forgotten Weapons examines reproduction XM-177 and GX-607 moderators by Liemohn Mfg. Historical data and live-fire tests show these functional devices offer measurable sound reduction, bringing short carbines closer to standard rifle noise levels, though they are legally classified as NFA suppressors.

Chapters

  1. 00:00Introduction to XM-177 Clones
  2. 00:54Liemohn Mfg Reproductions
  3. 01:10Historical Context & Purpose
  4. 03:26Live Fire Sound Testing
  5. 04:281968 Technical Test Data
  6. 05:18Internal Design & Durability
  7. 08:32Legal Status & ATF Ruling
  8. 11:05Pricing & Market Availability

Frequently Asked Questions

Do reproduction XM-177 and GX-607 moderators actually work?

Yes, reproduction functional moderators, like those from Liemohn Mfg, demonstrate a measurable reduction in sound, bringing the report of short-barreled carbines closer to that of standard rifles, according to 1968 test data and live-fire comparisons.

What was the historical purpose of the XM-177 and GX-607 moderators?

Developed in 1965 for use in Vietnam, these moderators were created by Colt to make the sound of short carbine barrels comparable to standard 20-inch rifles, addressing the excessive loudness of early short-barreled rifles in combat environments.

Are these moderators considered suppressors by the ATF?

Yes, the ATF ruled in 1975 that these devices are legally classified as suppressors because they reduce sound. This led Colt to recall them from commercial sales and necessitates NFA registration and tax stamps for current reproductions.

What were the measured sound reductions from the 1968 tests?

Original tests showed a standard M16A1 rifle at 161.7 dB, while an XM-177 clone equipped with a functional moderator registered between 159-160 dB, indicating a reduction in overall sound output.

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