Running Dry

Let's talk about bearing surfaces!

First a long word; lubriscosity.  It's a simple word.  It's how well two parts will slide on each other.

It's normally found in descriptions of lubricants, but it can apply to dry materials too.

Dissimilar materials sometimes have lubriscosity between them.  The oldest example I can think of is the ruby "jewel" in a timepiece.

Bronze and steel have something of the same effect.  The two metals just don't want to stick to each other.  It's not as slippery as, say, a film of oil keeping the parts from touching, but it will do.  This is exactly how a throw-out bearing in a manual transmission works.  Bronze bearing, spinning steel shaft.

Like metals do not have this effect.  Like metals want to stick to each other.  This is called galling.  This is why we put a film of lubricant between them.  If the parts can't touch, they can't stick!  Most dissimilar metals are this way as well.

Chrome, as mentioned in the AR example, was not selected because of its lubriscosity against aluminum.  It was chosen for three reasons, hardness, corrosion resistance and adhesion.

Here's a place where our rifleman is ALMOST right.  To this day there's a hard chrome plating on the inside of the bolt carrier.

Chroming the bolt and carrier was originally intended to keep them from rusting!  The goal was to make a minimum maintenance rifle, and chrome plating these parts protects them from rust.  The hardness for the gas chamber bore is a property he took advantage of in his design, but it's not the original reason chrome was specified.

Gene Stoner realized that pretty much any lubricant was toast where the gas rings seal against the wall of the bolt carrier's gas chamber.  So he chrome lined the chamber and used sacrificial parts to bear agains the hard chrome walls; the gas rings.  The rings provide the seal and the chrome plating keeps the rings from wearing out the bore of the chamber.  The stainless steel of the rings has OK lubriscosity against chrome so no lubricant is required (good because none will last).

Finally adhesion.  Carbon fouling doesn't stick to chrome very well.  Chrome plating makes the bolt and bolt carrier easier to clean.

You may have noticed that I didn't mention the lubricative properties of chrome against hard anodized 6061 T5 aluminum.  I didn't mention them because there's no advantage to using chrome against anodized aluminum over just using steel.  By the way, for the nitpickers, 6061 T5 is the AS DESIGNED material Armalite specified for the AR-15.  Mr Badge is a big advocate of as designed in his tirade.  Why are the upper and lower of the modern AR and M16 made from the more expensive 7057 T6 today?  Corrosion.  Once the anodizing is worn off (and it will be) 6061 starts becoming a flakey white crust and pretty soon your part has the structural properties of a soda-cracker.

And not one bit of the above matters at all against the as designed claim when compared to a tiny little anecdote from Mr Stoner himself.  When we was dragged out to Alaska to account for why the guns weren't working, among his list of things that were being done wrong was a lack of lubrication to the bolt carrier group.

This was reiterated during the Secord hearings.

For decades the people who designed the guns and just about anyone with some mechanical aptitude has looked at the moving parts and said, "lets put some oil here".  The idea that little to no lubrication is needed comes from the doctrines of an Army that stores rifles far more than it shoots them and a "white glove" inspection mentality that seems nearly impossible to eradicate.  You see, oil attracts dust and dust shows up on a white glove so only use just enough oil to keep rust from forming.