The CAR-15 rifle was the original; the M4 carbine is just a copy, and shouldn't exist.

1. The CAR-15’s place: a family of early carbines, not a one‑off origin myth

Colt’s CAR-15 program in the late 1960s produced a family of carbine‑length AR variants—compact, sometimes experimental carbines like the XM177—that were definitive precursors to later short‑barrel AR designs but always part of an evolving lineage rather than a single immutable “original” design ^{[1] [2] [6]}. Contemporary summaries explicitly describe “CAR-15” as a generic name for carbine variants made before the M4 era, underscoring that it was an early stage in a continuing platform evolution ^{[1] [7]}.

2. The M4’s genealogy: evolution through decades, not wholesale copying

The M4 carbine was developed in the 1980s and adopted in the 1990s as a shortened, purpose‑built evolution of the M16 family, incorporating different gas system lengths, barrel profiles, and features tailored for modern close‑quarters combat—changes that stemmed from lessons learned with CAR‑15/XM177 variants rather than mere copying ^{[3] [8] [9]}. Multiple sources note that the M4 built on the “spiritual ancestors” of the Vietnam‑era short carbines but went through formal government development programs (e.g., XM4 testing) before service adoption, which distinguishes it from being merely a derivative clone ^{[8] [9]}.

3. Technical and doctrinal differences matter

Key technical differences—such as carbine‑length versus rifle‑length gas systems, barrel lengths, and fire‑control arrangements—are repeatedly highlighted in contemporary comparisons and were reasons the military pursued the M4 as a distinct system for urban and close‑quarters operations ^{[8] [4]}. The M4’s configuration, production standards, and role as a service carbine made it operationally distinct from earlier CAR‑15 variants that were often experimental, limited‑issue, or optimized for special missions ^{[2] [10]}.

4. “Shouldn’t exist” is a normative judgment outside the technical record

Arguments that a weapon “shouldn’t exist” mix policy, ethics, and politics with engineering history; the documentary record in these sources records an iterative development path where each new carbine addressed specific tactical needs and tradeoffs—shorter length for maneuverability, different gas systems for reliability—rather than violating any clear technical or legal lineage ^{[4] [5]}. Whether a type of weapon ought to be produced is a separate public‑policy debate not settled by the historical development path documented here; those sources do not adjudicate moral or legal prohibitions about manufacture and use ^{[3] [11]}.

5. Competing narratives and commercial incentives

Some reporting emphasizes lineage to support particular brand or cultural narratives—Colt and other manufacturers marketed the CAR‑15 identity in part to reclaim the AR name, and later industry pieces trace a clean lineage to the M4 because that appeals to continuity and sales narratives ^{[7] [12]}. Conversely, enthusiasts and historians who emphasize differences between CAR‑15 and M4 do so to justify adoption and modernization choices; both perspectives reflect institutional and commercial incentives rather than a single objective verdict ^{[6] [12]}.

6. Bottom line: lineage yes, illegitimacy no

The factual record shows CAR‑15 designs were important and formative predecessors to modern carbines but do not make the M4 an illegitimate “copy”; the M4 represents a documented, iterative evolution with distinct design decisions and formal adoption after testing, which grounds its existence in a continuum of development rather than theft or error ^{[1] [9] [4]}. Public debate about whether such weapons should be produced or fielded belongs in the realms of policy, law, and ethics—domains not resolved by the technical‑historical sources provided here ^{[3] [11]}.