M4 type carbines are a very hot ticket for law enforcement and civilian self-defense these days. They are light, handy, compact and offer a greater level of performance than any pistol caliber carbine. Due to this fact, many law enforcement agencies are changing over from pistol caliber submachine guns for SWAT use to M4A1 type carbines. For patrol, a semi-automatic version of the M4A1 is an ideal choice. Ammunition parts and accessories are plentiful and reasonably priced. In fact, one of the greatest strengths of the M4A1 type carbine is its modular capability.

The AR carbine wasn’t originally intended to be a modular weapon, but it became so in the early 1990s when the Special Operations thor2Command (USSOCOM) developed the SOPMOD (Special Operations Peculiar Modification.) There are actually two versions of the M4 – the M4 Carbine, basically a short barreled version of the M16A2 with fixed carry handle and three round burst in addition to semi-automatic fire and the M4A1 with a fully automatic capability and a flattop receiver with a MIL-STD-1913 rail. It is this version that is used for the SOPMOD conversion and in semi-automatic form the one most used by law enforcement.

In the department where I serve as a reserve officer, every full-time officer is issued a semi-automatic M4A1-type carbine for patrol carry. Several full-time and reserve officers have purchased carbines of their own for personal and duty use. Many officers have taken advantage of the M4A1 type carbine’s modular nature to customize their issue carbines to suit their personal tastes.

Cops are probably the most underpaid people on the planet, so very few can afford to buy a ready made custom M4A1 type carbine, which can cost well over $2000. But because of the simplicity of the M4A1 design and ready availability of parts, a custom carbine can be built a step at a time on a budget. Every feature in this article can be purchased and installed as a “stand alone,” usually using common tools and generally without the help of a gunsmith. We installed every custom part of the M4A1 carbine featured herein in the family kitchen, after first obtaining dispensation from a very understanding wife.