On Colt

There's a raging debate, several actually, going on at AR15.com about what makes Colt ARs better than everyone else.

More reliable. Anecdotal testimony that they fail less than anyone else during tactical training courses like Gunsite. Few of these anecdotes include what broke on the "lesser" AR.

Chrome-Vanadium steel (CVS) barrel instead of 4150 steel. This one is a tough call since Colt is using a proprietary steel whose properties are not published. It could very well be better than 4150, it could be the same as 4150 but easier to make/machine. The information we need to make the call is not available, but I tend to let Colt have this one, especially since some makers are using 4140 steel!

Colts are Mil-Spec. Whether this is good or not depends greatly on circumstances. Both a Hummer and a Stryker are mil-spec. If someone is shooting small arms at me, I want the Stryker. If I get a fixed amount of fuel to get as far as I can, I want the Hummer. Mil-spec is simply the specifications drawn by the military defining what it is they will be purchasing. Since the color of both the parkerizing and anodizing is called out on the Mil-Spec, it's obvious that one can deviate from it without affecting quality. Materials are specified in some cases, sometimes better, more expensive, materials are available. Minimum performance criteria are specified, this is the hard one.  Mil-Spec calls for chrome lined bores and chambers, while this improves durability it is known to have an adverse effect on accuracy, which is better to have?

I got curious and have ordered a copy of:

MIL-C-70599A (Army) Carbine, 5.56-MM, M4
MIL-C-71186 (Army) Carbine, 5.56-MM, M4A1
MIL-R-63997B (Army) RIFLE, 5.56-MM: M16A2
MIL-R-71135 (Army) RIFLE, 5.56-MM: M16A2E3

Let's just see what they say in about a week, shall we?

Government Profile Barrel. A bit of history is required here. Eugene Stoner had two main goals in his design; first that the recoil forces would all act in one direction, down the axis of the bore and second that it be as light as possible. In pursuit of this goal, he removed as much of the barrel as he could, it starts at 1.000" near the chamber for about 1.500" then tapers to 0.841" over the next 0.750" and then tapers to 0.625" near the front sight base. The M16 and M16A1 continue with 0.625" to the muzzle threads. The M16A2 is 0.750" from the front sight base to the muzzle threads, but is identical under the handguards. One Colt Kool-Aid Drinker (CKAD) has made claims that this profile is specially designed for maximum strength under the stresses of heat and firing and bayoneting, and that he has done Finite Element Analysis (FEA) to prove it. Remember when I mentioned that Colt has not published the properties of their CVS? Without that information it is impossible to do an accurate FEA! Another glaring hole in his position is Mr Stoner didn't have FEA for his design, he had to calculate it manually, with a slide rule, it was the fifties after all.

The M16A2 barrel is thicker from the front sight base to the muzzle because of bone-head soldiers using their rifles as pry-bars, not to improve accuracy or reliability.

The M4 and M4A1 barrels have places where the barrel is cut down to 0.625" diameter to allow the mounting of an M203 grenade launcher, the rebated section is not tapered in, but ninety degrees, that would be a serious stress riser is Mr CKAD is correct about the profiles.

Non-Government Profile Barrels.  Most rifles on the market today have an HBAR (Heavy BARrel) profile.  That starts as 1.000" at the chamber for about 2", then tapers to 0.750" over the next 2" and then stays 0.750" to the muzzle threads.  Lightweight barrels are the same, but taper to 0.625".  There is more meat on an aftermarket barrel; and they are heavier.

Colt makes HBAR barrels too, so we don't really know what CKAD's point is.

Colt uses the Technical Data Package (TDP).  This is an internal Colt document that simply specifies how Colt will achieve the Mil-Spec.  It's their standards and practices.  Things like how threads will be let into the material are called out.  Time and temp to get the correct thickness on the anodizing.  Having and following the TDP would certainly make it easier to duplicate an M16, it's merely one path to the goal.  One example would be rifling, Colt may use broach cut rifling where an aftermarket vendor uses hammer-forged blanks.  After chroming, there is little difference.

Believe it or not, this is just scratching the surface!