The Bi-Poly by 8762e13 (Cal) is a 3D-printable lower receiver system for AR-15, AR-10, and AR-9 platforms, evolved from the Mono-Poly with improved ergonomics, durability, and wear resistance via compression limiters or key-stock reinforcements. Offered in “easy” and “hard” build variants, it supports standard and bufferless configurations, multiple grip styles, and Glock-mag AR-9s with LRBHO. Compatible with semi-auto builds and, where legal, full-auto components, the Bi-Poly is designed for maximum versatility across calibers and configurations, though exact compatibility may vary by upper and parts selection.