The Colt M4 Monolithic SBR is an 11.5-inch, 5.56 NATO short-barreled rifle built on Colt’s one-piece monolithic upper receiver (Colt part no. LE6943). The monolithic design carries a continuous rail from the back of the upper receiver to the front, which gives repeatable optic mounting that a separate handguard cannot match. The barrel floats free of the rail for consistent accuracy, and Magpul MBUS folding sights are fitted. It ships with one 20-round magazine for a 20+1 capacity and runs semi-automatic on Colt’s direct gas impingement system. It suits a shooter who wants a rigid, compact Colt for optics-heavy duty or defensive use.

Key Specifications

• The chambering is 5.56 NATO, the standard M4-pattern cartridge.
• Barrel length is 11.5 inches, compact for vehicles and close quarters.
• The upper is a one-piece monolithic receiver with a continuous rail from the rear of the upper to the front.
• The barrel is free floating, isolated from the rail for consistent shot placement.
• Capacity is 20+1, and one 20-round magazine is included.
• Sights are Magpul MBUS folding sights, which co-witness with a red dot or serve as primary irons.
• The action is semi-automatic on Colt’s direct gas impingement system.
• The barrel is chrome lined, Colt’s standard for corrosion resistance.
• The bolt is HP/MPI tested, Colt’s high-pressure and magnetic particle inspection.

Frequently Asked Questions

What does the monolithic upper do? It joins the receiver and rail into one forged piece with a continuous top rail, so optics hold zero across the receiver-rail joint and the barrel floats free.

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 short-barreled rifles. It transfers on a Form 4473 with a background check through a Class 3 (SOT) dealer. State and local laws still apply. Taking an SBR across state lines still requires an approved ATF Form 5320.20.

What magazine comes with it? One 20-round magazine. The rifle accepts standard AR-15 pattern magazines.

Buy the Colt M4 Monolithic SBR, 11.5-Inch

As of October 9, 2026, this short-barreled rifle 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 Colt‘s short-barreled rifles lineup and our Lubbock, Texas team will handle the transfer.