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Geissele Automatics
08-553S-Geissele
The Geissele Super Duty MOD1 .300 BLK 8" 1:7" CHF Chrome Lined Bbl DDC 08-553S upper is purpose-built for suppressed, short-barreled applications where .300 Blackout does its best work. It ships as a genuinely complete assembly, BCG, charging handle, and muzzle device all installed, so a compatible registered SBR or pistol lower is close to the only thing standing between this and a finished build.
The 8" barrel is cold hammer forged and chrome lined with a 1:7 twist, stabilizing both subsonic and supersonic .300 Blackout loads without needing a barrel swap between the two. What really sets this Geissele Super Duty MOD1 8 upper apart is the gas system: instead of a standard carbine-length setup, Geissele runs its patented Phased Array gas system with the Tri-Port design, tuned to a Custom Pistol length specifically for this barrel. That precise gas metering matters even more in a short-barreled, suppressed .300 BLK build than it does on a standard 5.56 carbine, where timing gets a lot less forgiving.
A 7" Super Modular Rail MK16 mates to the upper through Geissele's center aligning tab, keeping the whole package compact without sacrificing M-LOK real estate for lights or grips. Cycling runs through Geissele's Nanoweapon-coated Reliability Enhanced BCG, and the HUXWRX Flash Hider-QD muzzle device threads on at 5/8x24, the correct pitch for .300 Blackout muzzle devices and suppressors rather than the 1/2x28 used on 5.56 builds.
At approximately 3.3 lbs and finished in Desert Dirt Color, this Geissele upper receiver is ready to drop onto a compliant lower.
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08-553S
