Why can't bores be boron carbide coated?  We like chrome lining because it's better than the soft steel gun barrels are made out of, so the bores last longer.  But we don't like chrome lining because it's thick and therefore inconsistent, so in theory it will reduce accuracy.

    But boron carbide is more wear resistant than hard chrome, and it is only 1-2 microns thick, which is somewhere around a millionth of an inch.

    So...  it beats hard chrome because it isn't inconsistent and it won't reduce accuracy, and it beats hard chrome because it's even more wear resistant.

    Oh, boron carbide also has very low static and dynamic coefficient of frictions, so don't have to worry about that.

    Seems like it would be great for bores.  How come nobody does it?

It might have something to do with the vapor deposition process being unable to get into a long narrow hole such as a 0.223" bore well enough for full coverage.

But that is just a guess, I'm no expert.

someone told me to tell you they said,

"it is abrasive!"

Expense maybe?

It is abrasive, flaky, and does not stand to flexing.

Why not Titanium nitride? Its used to hard coat drill bits and high end motorcycle forks.
Seems to wear well, its extremely thin, and I think it has a lo coefficient of friction too.
It actually replaced chrome plating on forks.
BP

I'm no metalurgist, but several years age while working in Houston, we used a plasma torch to blow Stellite on the face of gatevalve gates for the oil drilling industry. These faces were blown on undersize gates and then surface ground down to spec. The stuff is tremendously slick and abrasion resistant ( like 10,000 PSI baroid /saltwater/gas flow hitting them directly) with very little wear. I know the M-60's had Stellite chambers, could you possibly coat an oversize bore with a torch wand passed through the bore and then rifel to spec???

It isn't abrasive; that's like saying TiN or TiCN coatings are abrasive.  B4C is often used AS an abrasive because it is very hard (it is used in large grains as an abrasive, but that is not what we are talking about here, we are talking about coating the bore).  HRC 95, Mohs 14.  The only thing harder is diamond and cubic boron nitride (actually, at super-high temps, B4C is even harder than those).

I also disagree that it is flaky and doesn't stand to flexing.

"It has a four point flexural strength of 50,000 - 70,000 psi and a compressive strength of 414,000 psi." -- from a webpage

I have never heard of B4C, TiN, or TiCN flaking off of knives.  Nor have I heard them flaking off of tools that are dented.  In fact, a buddy of mine with TiN tools says that if he dents the tool, the coating dents with it.

Thus, I am going to have to disagree with Monel_Funkawitz.

I don't see how anything 1 micron thick can be abrasive, low coefficient of friction or otherwise.

BTT because it's an interesting topic.



Cheers,
Chris

    Hello.  I found a page where someone put it into firearm use, but only exterior -- no bore.

www.blindhogg.com/boroncarbide.html

Note that it easily beat all other coatings, including hard chrome.

Hello.  For you non-knife guys that don't know what B4C is, here's it being used on knives:

www.simonichknives.com/covert.htm

It's much like any plating process.  Getting down a long, skinny hole is difficult.  Chrome plating is a little easier, because a wire centered in the bore can be used as an anode while the plating solution is pumped through the bore.

TiN, and I'll guess boron carbide, is a vacuum deposition process.  As it goes down a hole, it loses material so the buildup is thicker at the beginning and thins out as it goes deeper.  Doing just the chamber is probably realistic.  Maybe even getting a bit of the throat.  That might well make a match bore much longer lived.  It will cost a few $ though.  The equipment is expensive and probably not big enough to do barrels.  That means custom vacuum chambers and that means $.

I don't think chrome bores are done by the electrochemical process.  Most I have seen in the M16 series have had only ~1/2 of the extension locking lugs plated, indicating the receiver extension was installed and barrel finished before plating.  I woulf find it very hard to see how any electrochemical process could do that.

I tend to think its done via vapor deposition, primarily to reduce hydrogen entrapment (major no-go in the barrel steel) as the steel can be quite hot during this process unlike electrochemical where temps are limited by the aqueous solutions.

As far as the other harder materials, they lack the elasticity of chrome and do not bond with the tenacity of Cr.  Flaking would be a problem.

Chrome CAN be applied with great uniformity, its just that it can also be fouled up.  Only testing with real ammo will show a good job and only after the chrome has been smoothed out by firing.

I read on cruffler.com that chrome lined bores are less accurate, 'cause metal has to be removed, and it can never be applied at the same tolerances as match bores are cut to.

I found this on a 1911 website...

BORON CARBIDE THIN FILM CERAMIC COATING Ultra-Hard Coating with Extraordinary Wear and Corrosion Resistance that Won't Pit. Natural Affinity to Retain Presented lubricants. Outstanding Corrosion Protection. Impervious to Most Harsh Chemicals Acids and Bases, Virtually Eliminating Corrosion While Maintaining Lubricity. Excellent Resistance to Chipping, Cracking and Peeling. Boron Carbide Coats to a Sharp Edge. It will Not Distort or Build Up in Corners. Thermal Resistance Reaching 2732 degrees F or 1400 degrees C. Anti-Reflective - On Matte and Blasted Finishes - Desirable for Maximum Covert Carry. Physical Vapor Deposited - Coats the Entire Component at No Additional Charge Darrell Lewis Bodycote Diamond Black, Inc. 100 Somerset Drive Conover, NC 28613 USA Tel: (828) 327-7442 Ext. 3103 Fax: (828) 322-4636 e-mail: [email protected]

Says no chipping, cracking, or peeling.  I think that means it won't flake off.

Well, I e-mailed Bushmaster about a week ago, asking them if it can be done.  I never received a reply, so I posted on here.  Still no reply from them.  Oh, well.  Their customer service always has been like that.

Maybe if I get money, I can send something to this Darrel Lewis fellow and have him do the whole deal, bore included...  then I'll try putting some rounds through it, and I'll let you know if the barrel explodes and sticks fragments into my eye or what not.

Has anyone tried Melonite or QPQ as a bore process?  It is very durable, hard, corrosion and wear resistant.
I have heard that one dowmfall is that it has to be on a virgin barrel, never been fired, not even test fired.

http://www.finishing.com/kolene/qpq/

Hello.

I have good news.  I asked Metal Smith if it can be applied to bores.  He said,

yes there is a process for doing bores but its not done in the NC plant, bores are the next step, but it may not be worth the effort, Pete

So I guess they plan to do bores eventually.  I am happy to hear that, I would like to try it out.

I am not sure why he said it can't be done yet, since I thought it was vapor deposition, so it shouldn't matter outside or inside.  Oh well.  If they are planning on doing it, that is still good news.

I hope they do decide to coat bores. If they do I am sending my toris to them for testing. If it turns out good I will probably have everything I own coated in the stuff, including my Benchmade 710BT and whatever fixed-blade knife I end up getting in the future.

That way they can do it all at the same time and reduce the cost to me (at least I hope it will work out that way).

If you send in the 710, it will void the warranty because you will have to disassemble it.  You will have to find a way to remove all that BT2 as well.

I work with carbide alot, and it does not stand flexing AT ALL.  Carbide cannot withstand shock, impact loads,  or wide and quick temperature extremes.  When confronted with the above, it chips and carbide coatings will peel off. That is why you never see carbide coated drills.

When given a constant load, carbide is great.  Unfortunately, no gun barrel is like this.  Also, with the cost of boron carbide coating, I can get two or more barrels for the same price, of which will last longer than the exotic coated one.

I would rather have my money invested in better quality steel/parts rather than some goofy ass teflon/carbide/plutonium coated bore.