The GSL Fat Man 9mm suppressor is a full-auto rated, aircraft-grade aluminum can that GSL Technology built for MP5 and three-lug barrel submachine guns (brand part no. FM-100-SUP). It mounts by the Tri-Lock system and ships with an H&K tri-lug mount. Beyond 9mm, GSL rates it for .38 Special, .357 Magnum and subsonic .300 Blackout, so it also serves 9mm pistol-caliber carbines. GSL lists 34 dB of sound reduction from a can that weighs 11 ounces.

Key Specifications

• Caliber rating is 9mm, .38 Special, .357 Magnum and .300 Blackout (subsonic only).
• GSL publishes a sound reduction of 34 dB.
• Length is 6 inches, compact enough for a subgun.
• Diameter is 2 inches, the fat body the name refers to.
• Weight is 11 ounces, light for a full-auto rated pistol-caliber can.
• Materials are aluminum and stainless steel, with a hard coat anodized finish.
• The mount is Tri-Lock, and an H&K tri-lug mount is included.

Frequently Asked Questions

What firearms does it fit? MP5-pattern and three-lug barrel submachine guns with the included H&K tri-lug mount. GSL offers 1/2×28, 1/2×36, 5/8×24, 9/16×24, Scorpion 18mm and UZI FS mounts separately.

Do I need ATF approval to buy this? No. As of October 9, 2026, ATF no longer requires Form 4 approval, registration or a tax stamp for suppressors. It transfers on a Form 4473 with a background check through a Class 3 (SOT) dealer. State and local laws still apply.

Does it need any maintenance? GSL notes that a disassembly tool is available for purchase and that the piston may need silicone grease to keep moving after prolonged use.

Buy the GSL Technology Fat Man 9mm Suppressor, Tri-Lock Mount

As of October 9, 2026, this suppressor transfers on a Form 4473 with a background check at your Class 3 (SOT) dealer, with no Form 4 or tax stamp; state and local laws still apply. Order through GSL Technology‘s silencers and suppressors lineup and our Lubbock, Texas team will handle the transfer.