Mac n Cheese [2.5] Build Kit

Mac n Cheese [2.5] Build Kit Overview

The Mac n Cheese [2.5] Build Kit delivers everything you need to build a complete 3D printed M11-pattern pistol caliber carbine. This isn’t a hardware-only kit—it includes a complete 9mm side-cocking MAC-11 upper, AR15 fire control group with safety, stainless steel LRBHO components, and all the hardware required to finish your build. Print the lower, open the box, assemble.

The Mac n Cheese is a printable ambidextrous M11 lower receiver that introduced the first-ever Last Round Bolt Hold Open (LRBHO) system to the M11 platform. Version 2.5 brings significant improvements including a completely redesigned magazine catch, no-feedramp geometry, and an adjustable overtravel stop. Compatible with standard full-size 9mm M11 uppers, the Mac n Cheese accepts Glock magazines and uses a familiar AR15 fire control group.

What Makes the Mac n Cheese [2.5] Different

Integrated LRBHO – A Platform First
The Mac n Cheese pioneered Last Round Bolt Hold Open functionality on the M11 platform. When the magazine runs dry, the bolt locks back automatically—no more guessing whether you’re empty. The stainless steel LRBHO components included in this kit are precision-made for reliable function.

Completely Redesigned Magazine Catch
V2.5 addresses one of the biggest complaints about V2: the magazine catch now actually works. This isn’t a minor tweak—it’s a complete redesign that ensures positive magazine retention and reliable release. Combined with Glock magazine compatibility, reloads are fast and familiar.

No-Feedramp Design
Based on input from PY2A, Version 2.5 eliminates the feedramp entirely. This streamlined approach improves reliability while simplifying the printed geometry. The result is cleaner prints and more consistent feeding.

Ambidextrous Controls
The Mac n Cheese lower is fully ambidextrous from the factory. Left-handed shooters get the same experience as right-handed shooters without modifications or compromises.

AR15 Fire Control Group
Instead of proprietary trigger components, the Mac n Cheese uses a standard AR15 FCG with safety selector. Parts are common, affordable, and well-understood. The included FCG comes ready to install with the safety already fitted.

Adjustable Overtravel Stop
Fine-tune your trigger feel with the integrated adjustable overtravel stop. Dial in a crisp, short reset for faster follow-up shots and improved precision.

What’s in the Mac n Cheese [2.5] Build Kit

Core Components
Complete 9mm side-cocking MAC-11 upper with bolt and threaded barrel, stainless steel LRBHO assembly, AR15 fire control group with safety selector, and AR15 grip with grip screw. These are the functional components that turn your printed lower into a working firearm.

Assembly Hardware
5/16 clevis pin, M3x30 screw, M3x20 screw, three M4 grub screws, M4x35 screw, M4x45 screw, M5x70 screw, two M4 nuts, and one M5 nut. Everything required for complete assembly.

What’s in the Box