The UBAR 3/X is a robust, battle-tested 3D printable AR-15 lower receiver that showcases nearly a decade of design refinement. Reinforced with simple yet highly effective hardware, it’s built to withstand serious abuse, from drop tests to field use.
The UBAR3 and UBARX variants cater to both traditional and integrated pistol grip preferences, offering strength and compatibility with most mil-spec AR-15 uppers.
In the Wild
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Features of the UBAR 3/X
Unmatched Reinforcement: A U-Bolt clamps the buffer tower, while two rod-end eye bolts secure the front takedown lug, making this one of the strongest printable AR lowers available today.
Customizable Variants: Choose from 16 combinations including carbine/rifle buffer tube support, anti-walk hammer pin compatibility, and forward assist cutouts.
Print-Friendly and Tested: Designed for 3D printing, especially in PLA+, and tested extensively with everything from PMAGs to LaRue uppers.
UBARX builds offer a monolithic pistol grip for added strength, while UBAR3 supports removable grips. Thoughtful features like enhanced reinforcing humps and optional push-button safety make the build both user-friendly and durable.
Hardware and Tools Required
Hardware
- AR-15 upper (with BCG & charging handle)
- AR-15 Lower Parts Kit (minus trigger guard & takedown pins)
- Carbine or rifle buffer tube and buffer
- Stock (e.g., B5 Bravo or printable)
- U-Bolt: 1/4″-20 thread, 1-1/8” ID
- Rod-End Eye Bolts: 1/4” x 1-3/16” Flat-Shoulder
- Locking nuts, detents, springs, extended pins (or equivalent)
Additional Parts
- Optional: Push-button safety for clearance
- UBARX only: 1/8” x 1” roll pin or substitute
3D Printed Parts for the UBAR 3/X
You’ll choose between UBAR3 (removable pistol grip) and UBARX (integral grip) variants. All 16 permutations are available, so pick the one matching your preferred configuration: buffer type, forward assist cutout, and pin style.
Files are pre-oriented and scaled correctly. Print in eSun PLA+ or better. Stick to recommended print settings for best results. Changing orientation or scale can mess up fit and function!
Tools Required
- Drill with bits: 1/8”, 1/4″, 5/32”, 7/32”, 3/8”
- 1/8” punch, hammer
- Screwdriver or Allen key
- Dremel with cutoff wheel or hand file
- 1/4-28 tap (for UBAR3 grip screw)
- Optional: Needle-nose pliers, long Allen key, magnetizer
Filename Instructions
Conclusion
The UBAR 3/X is the culmination of years of evolution in DIY firearm design. Whether you’re looking for modularity or brute strength, this platform gives you a reliable, high-performance AR-15 lower receiver.
Choose your variant, print with care, reinforce it right, and you’ll have a lower ready to go to war (or at least the range).
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