UBAR2 AR15 Lower

ubar 2 ar15 lower

UBAR2 AR15 Lower STL Files

3D Printed UBAR2 Lower Printable AR15 Lower Reciever

UBAR2 AR15 Details

The UBAR2 AR15 lower is one of the most durable and solid AR15 lower frames available to 3D print online.

The UBAR2 is reinforced around the buffer tube and at various other common “problem” points to increase the round capability.

Maintaining the integrity of AR15 lowers and not causing breaks, failures, and “out of spec” problems has been the goal of 3D printed AR15 developers from the get-go.

The UBAR2 is the latest version of the AR15 printed UBAR (named after its signature U-Bolt reinforcement parts) with even more stability around the takedown lugs and buffer tower.

The UBAR2 has also been designed to be compatible with a wider range of AR15 uppers.

Shop UBAR 2

3DGB has stocked everything you need to complete your UBAR 2 build.

Buy UBAR & UBAR2 Parts Kit

The UBAR2 Parts Kit is a revolutionary new parts kit that is designed to enhance the functionality and performance of your UBAR2 3D printed AR-15.

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UBAR2 AR15 in the Wild



UBAR2 AR15 Test Fire
UBAR AR15 Lower Release Announcement

UBAR2 AR15 Tech Specs

There are eight UBAR2 variants are available for download.

Four of the variants are the UBAR2, four are the UBAR2C – the “C” designation indicates that the lower has a little extra clearance.

Both the UBAR2 and UBAR2C have four sub-variants – there are high-shelf options and low-shelf options.

If you plan on using an FRT trigger, or another device that requires a low-shelf receiver, print one of the low-shelf models.

Otherwise, the standard lowers will be stronger (since lowering the shelf increases stress concentration in the lower).

For all the high and low-shelf variants, there are two sub-variants – lowers that have a cutout for the forward assist, and lowers that do not.

If you have a forward assist installed on your rifle, print the forward assist version. If you have a side charging AR, one without a forward assist, or you removed/plugged your forward assist.

Required Parts for the UBAR2 AR15 3D Build

Complete AR15 upper – any barrel length, gas system length, etc. The UBAR has no issues handling big-bore AR15 uppers.

Standard AR15 carbine lower parts kit (read the introduction if you want to use a rifle lower parts kit):

  • Fire control group – hammer, trigger, disconnector, plus the springs for each of these
  • Safety selector, detent, and spring
  • Magazine catch, catch spring, and button
  • Buffer retainer, buffer retainer spring
  • Buffer tube – try and find a “mil-spec” buffer tube
  • Buffer tube castle nut and locking plate
  • An AR15 pistol grip – I really like B5’s Type 23 grip, and it fits perfect on the UBAR. You can always print a grip if you’d like.
  • An AR15 stock – if you are using a carbine tube

UBAR2 Reinforcement Parts Required

1x U-Bolt – The U-Bolt required is a 1/4″-20 thread, 1-1/8” ID. I prefer carbon steel to stainless steel

2x 1/4″-20 nuts and a nut plate – for the U-Bolt, but your U-Bolt will usually come with these.

2x 1/4″ x 1-3/16” Flat-Shoulder Rod-End Eye Bolts – these are somewhat uncommon size bolts and are tricky for bolt makers to produce, and tend to be pretty expensive.

Tools Required

You will need the following basic tools:

  • 1/4″, 5/32”, and 3/8” drill bits
  • hammer
  • 1/8” punch
  • screwdriver or Allen key to install your pistol grip screw
  • battery powered drill
  • Dremel tool with a cutoff wheel (or a metal file)
  • 1⁄4-28” tap
  • needle-nosed pliers (optional)

Suggested 3D Print Settings

The following setting have been tested for the best results when 3D printing the UBAR 2 AR15 lower (PLA+ filament used):

Walls: I used 8, but you’re free to use whatever works best for your 3D printing setup.

Nozzle: 0.4mm Layer Height: 0.15mm or 0.16mm

Temp: 230/60C Infill: 100% Recommended – while the UBAR2 might not need 100% fill, this ensures that you won’t end up hurting the lower if you overtighten anything.

Supports: On/full (tree supports are ok)

Cooling fan: 20% normal, 50% on bridges. Off for the first 10 layers. Keep the fan speed low to prevent warp.

Bed Adhesion: gluestick or hairspray is recommended

All STL files are oriented and scaled properly, and changing their scale or orientation may result in your parts not fitting/working properly.


All other settings can/should be left as default or whatever you know works best with your printing setup.

Frequently Asked Questions

Where can I buy a UBAR2 reinforcement kit?

There are various providers and you can even gather all of the UBAR2 parts yourself at a local hardware store.

Pre-packaged UBAR2 reinforcement kits can also be found here.


The UBAR2 is one. of the best available AR15 lowers and has Ivan’s signature and extremely thorough and detailed documentation included.

IF you are looking to get started 3D printing your own AR15; give the UBAR2 a try!

Is something missing or incorrect?

DISCLAIMER: 3D STL files are for learning and documentation purposes only. The users of this website and files need to be aware of all applicable local, state, federal and regional laws. 3D Gun Builder does not encourage, condone, or promote any illegal activity.

3D Gun Builder (3dgunbuilder.com) does not host, provide, develop, and/or have any affiliation with the firearm STL files or 3dgunvault.com. All files are hosted by a third party.

Dan M.
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