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The Aero M4E1-T Complete Upper in 13.9″ 5.56 CMV Mid delivers a ready-to-run upper receiver assembly built for shooters who want a compact, lightweight package without sacrificing modularity or build quality. Aero's M4E1-T platform combines a precisely forged upper receiver with a 13.9″ mid-length barrel and their proven ATLAS R-ONE handguard system—everything you need to complete a capable rifle for home defense, short-range competition, or compact duty use.
The M4E1-T upper receiver features Aero's enhanced forging that delivers a billet aesthetic while maintaining the durability of a forged component. The integrated M4 feedramps, picatinny rail profile, and laser-engraved T-marks work seamlessly with modern furniture and optics. A low-profile gas block and mid-length gas tube keep the sight line clean and the profile trim, while the threaded upper receiver design allows flexibility for future upgrades.
The 13.9″ barrel is constructed from 4150 CrMoV steel with a QPQ hardened finish, giving you a handy overall length without excessive velocity loss. The 1/7 twist rate handles a wide range of 5.56 ammunition, and both the barrel and bolt assembly have been HP and MPI tested for reliability. Aero's ATLAS R-ONE handguard wraps the barrel with a slim 1.3″ inner diameter, full-length top picatinny rail, and QD sling attachment points at 3, 6, and 9 o'clock—plenty of real estate for lights, lasers, or vertical grips while keeping weight down.
This complete upper arrives fully assembled and ready to drop onto a compatible lower receiver. Note that it does not include a bolt carrier group or charging handle—you'll source those separately to match your build preferences.
| Caliber | 5.56 NATO |
| Barrel Length | 13.9″ |
| Barrel Material | 4150 CrMoV with QPQ hardening |
| Twist Rate | 1/7 |
| Gas System | Mid-length |
| Gas Block Journal | .750″ |
| Upper Receiver | M4E1-T threaded, forged |
| Handguard | ATLAS R-ONE, 12.7″ |
| Handguard ID/OD | 1.3″ / 1.5″ |
| Flash Hider | A2 standard |
| Takedown Pin Holes | .250″ |
The M4E1-T upper is compatible with any mil-spec AR-15 lower receiver. The threaded upper design works with standard lower-to-upper interfaces.
This assembly does not include a bolt carrier group or charging handle. You'll need to source those separately to complete your rifle build.
The 13.9″ barrel length keeps overall rifle dimensions compact while the mid-length gas system maintains reliability and cycle control. This configuration works well for home defense, short-range tactical use, or competition applications where a shorter platform is an advantage.
The ATLAS R-ONE is a slim, lightweight handguard with a full-length top picatinny rail and QD sling attachment points at 3, 6, and 9 o'clock positions. It's compatible with low-profile gas blocks and provides plenty of mounting real estate while maintaining a streamlined profile.
The Aero M4E1-T Complete Upper in 13.9″ 5.56 CMV Mid delivers a ready-to-run upper receiver assembly built for shooters who want a compact, lightweight package without sacrificing modularity or build quality. Aero's M4E1-T platform combines a precisely forged upper receiver with a 13.9″ mid-length barrel and their proven ATLAS R-ONE handguard system—everything you need to complete a capable rifle for home defense, short-range competition, or compact duty use.
The M4E1-T upper receiver features Aero's enhanced forging that delivers a billet aesthetic while maintaining the durability of a forged component. The integrated M4 feedramps, picatinny rail profile, and laser-engraved T-marks work seamlessly with modern furniture and optics. A low-profile gas block and mid-length gas tube keep the sight line clean and the profile trim, while the threaded upper receiver design allows flexibility for future upgrades.
The 13.9″ barrel is constructed from 4150 CrMoV steel with a QPQ hardened finish, giving you a handy overall length without excessive velocity loss. The 1/7 twist rate handles a wide range of 5.56 ammunition, and both the barrel and bolt assembly have been HP and MPI tested for reliability. Aero's ATLAS R-ONE handguard wraps the barrel with a slim 1.3″ inner diameter, full-length top picatinny rail, and QD sling attachment points at 3, 6, and 9 o'clock—plenty of real estate for lights, lasers, or vertical grips while keeping weight down.
This complete upper arrives fully assembled and ready to drop onto a compatible lower receiver. Note that it does not include a bolt carrier group or charging handle—you'll source those separately to match your build preferences.
| Caliber | 5.56 NATO |
| Barrel Length | 13.9″ |
| Barrel Material | 4150 CrMoV with QPQ hardening |
| Twist Rate | 1/7 |
| Gas System | Mid-length |
| Gas Block Journal | .750″ |
| Upper Receiver | M4E1-T threaded, forged |
| Handguard | ATLAS R-ONE, 12.7″ |
| Handguard ID/OD | 1.3″ / 1.5″ |
| Flash Hider | A2 standard |
| Takedown Pin Holes | .250″ |
The M4E1-T upper is compatible with any mil-spec AR-15 lower receiver. The threaded upper design works with standard lower-to-upper interfaces.
This assembly does not include a bolt carrier group or charging handle. You'll need to source those separately to complete your rifle build.
The 13.9″ barrel length keeps overall rifle dimensions compact while the mid-length gas system maintains reliability and cycle control. This configuration works well for home defense, short-range tactical use, or competition applications where a shorter platform is an advantage.
The ATLAS R-ONE is a slim, lightweight handguard with a full-length top picatinny rail and QD sling attachment points at 3, 6, and 9 o'clock positions. It's compatible with low-profile gas blocks and provides plenty of mounting real estate while maintaining a streamlined profile.
