Purpose-Built 10.4-Inch Barrel for the FN PS90
The CMMG 57DF1C7 is a 10.4-inch replacement barrel designed for a lawfully registered FN PS90 short-barreled-rifle configuration. It preserves the PS90 platform’s original 5.7x28mm chambering while replacing the extended factory carbine barrel with a compact barrel manufactured specifically for the platform.
CMMG specifies a 1:9 twist, MT contour, 4140 chrome-moly steel construction, SBN surface treatment and M12x1LH muzzle threads. The listed weight is two pounds.
National Firearms Act Configuration
Installing this 10.4-inch barrel on a conventional stocked FN PS90 will create a short-barreled rifle regulated under the National Firearms Act. The firearm must already be lawfully registered in the appropriate configuration before the short barrel is installed.
For a nonlicensee making an SBR from an existing PS90, this ordinarily means receiving approval of an ATF Form 1 before making the firearm. Purchasing or possessing the barrel does not register the firearm or authorize installation. State and local restrictions may impose additional requirements or prohibit the resulting configuration.
5.7x28mm Chamber and 1:9 Twist
The barrel is chambered for 5.7x28mm and uses a 1:9 twist rate. These specifications are published by CMMG specifically for this FN PS90 barrel rather than for one of the company’s AR-pattern 5.7mm barrel and bolt-carrier kits.
This barrel should not be confused with a 9mm AR barrel, a CMMG Mk4/Mk57 barrel or a general-purpose AR-15 component. It is a platform-specific PS90 barrel.
4140CM Steel with SBN Treatment
CMMG lists the barrel material as 4140CM with an SBN treatment. The salt-bath-nitride process treats the steel’s surface to improve wear and corrosion resistance without applying a thick external coating.
This current specification supersedes older third-party descriptions that may refer to different steel, chrome lining or a phosphate finish. Use the specifications associated with current manufacturer part number 57DF1C7 when describing the barrel.
M12x1LH Muzzle Threads
The muzzle uses M12x1LH left-hand threads. CMMG offers a P90-style flash hider and an M12x1LH-to-1/2x28 PS90 thread adapter separately.
The barrel does not include a muzzle device or thread adapter. Select the appropriate component for the intended configuration and verify thread direction, caliber clearance, mounting requirements and suppressor compatibility before use.
FN PS90-Specific Fitment
This barrel is intended for the FN PS90 platform. It is not an AR-15 barrel and should not be selected for a CMMG Banshee, Dissent, Resolute, Mk4, Mk57 or another firearm simply because that firearm is also chambered in 5.7x28mm.
PS90 barrel replacement involves firearm disassembly and configuration considerations beyond an ordinary drop-in accessory change. Installation and final inspection should be performed by someone qualified to work on the FN PS90 platform.
CMMG Lifetime Quality Guarantee
CMMG backs its products with the company’s Lifetime Quality Guarantee. Warranty coverage and remedies are administered by CMMG according to its current terms and procedures.
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