To preface this, let me state that I served in the Marine Corps as a rifleman and that I carried a FN M16A4 in Iraq. The above picture is of the rifle I carried in Iraq.
I see online that some people have a hardcore love for the M16A4. In reality, it is not that good. Please don’t get me wrong it isn’t a bad rifle, but it is not a great one.
When considering the M16A4 uses as a combat rifle it is ok, but not as flexible as a M4. If you employ the M16A4 as a battle rifle, like the M1Garand, M14, and M16A2 that preceded it, it is great. However a battle rifle is not suited for all combat. The longer length of the M16A2 & M16A4 along with the fixed stock, makes for a less then ideal rifle for close quarters battle or for use with body armor. Its’ 40 inches of length makes the rifle more awkward when egressing vehicles.
The main benefits of the M16A4 over the M4 are higher muzzle velocity and longer sight radius. The benefits of increased sight radius are negated if we use optics. While more velocity is always nice, it is shot placement and bullet selection that is very important. Outside the military, we are not limited to M855 ball ammunition, and there are plenty of alternative that will function excellently in shorter barrels.
For a civilian, I can see why someone would want to reproduce a military rifle. However from a cost effectiveness standpoint, building a M16A4 clone is silly. Few companies make M16A4 style uppers, and there is good reason for that; they just don’t sell well. The Knights M5 RAS quad rail used on the rifle runs about $320 dollars new. For far less then that you can get a lighter, cheaper, free float rail. The Government profile of the M16A4 combined with a heavy non-freefloat rail does not make for the best accuracy or consistency. A proper M16A4 clone is neither accuracy enough for precision competition, nor as handy as a M4 style carbine.
While I was in the Corps, there was a big mentality that the M4 was just such an inferior weapon system. I believed this for a long time, till finally I started to realized that if the entire Army was fielding M4s, it can’t be junk. However our Army does make mistakes, but other groups like the SEALs, some of the British, German, Irish, and Australian special forces, etc. Many elite forces around the world choose the M4 or variants(like the C8SFW) for their mission over their own countries standard issue rifle, or full length M16s. Clearly the M4 has the reliability and capability for those end users mission.
The M16A4 is a battle rifle, however the M4 carbine is a versatile jack of all trades that is better choice for most individuals.
Picture of my last M16A4 clone rifle before I finally decided to move away from the M16A4 platform completely.