Why Moly/Ws2/hBn Please

[Greg110]

Gentlemen,
I understand all these coatings reduce friction and therefore heat and both of these things will extend barrel life. Are these the primary reasons for coating bullets, or have I missed something perhaps?

 

[Heavies]

I mostly use it (HBN) to keep fouling down during long strings of fire, so the rifle can keep consistency all day without cleaning.
Interested in what others have to say as well.

 

[RonAKA]

Harold Vaughn wrote an interesting book called Rifle Accuracy Facts. You can find a review of it at the link below. It is about half way down the page.

http://www.6mmbr.com/bookreviews.html

In the book he presents his theory that moly does not in fact reduce the friction between the barrel and bullet. While it is accepted that a moly coated bullet reduces the velocity for the same powder charge, the common assumption is that this is due to them being more slippery and don't allow the pressure to build up, so velocity suffers unless you add more powder.

Vaughn's theory is that the moly coating is vapourized right after ignition, and the vapourization effect reduces the heat of combustion, and thus pressure. So, essentially it is acting as a flame retardant. His argument was compelling enough to convince me to forget the idea of using moly coated bullets.

 

[jo191145]

Never used much moly and did'nt think much of it when I did.
WS2 was much better than moly.

I now use HBN for EXACTLY the same reasons Heavies mentioned.
Plus its so much easier to apply.

Actually I never put a patch down either of my point blank rifles last season
About 400 rds each.

You do have to search for the correct powder to pull that off.
Not just any powder will let you get away with it.

 

[spclark]

I used moly prior to learning about hBN & figuring out a way to home-coat bullets in a manner that replicates the coating supplied by D. Tubb. Not so much to reduce friction per se but to reduce the forces needed to swage a fired bullet into the lands & grooves, the better to withstand the subsequent high-speed path down range.

IMHO achieving such an effect contributes to diminished bullet deformation which then improves trajectory consistency shot to shot.

I'm not sure I can agree with Mr. Vaughn's theory; do sufficient combustion gasses pass across the coated bearing surface of a bullet to vaporize the coating before it enters the bore? I know some shooters used to augment propellant charges with moly powder, rather than or in addition to using coated bullets, so there may be some truth to the retardant effect but that seems an extreme approach.

Also - combustion products of sulfur-bearing compounds tend to become corrosive when sufficient water vapor is present. Use of moly (or WS2) may contribute to increased opportunity for barrel corrosion unless protective measures are used, since moly and WS2 (aka DANZAC, also a sulfur-bearing compound) both have far lower breakdown temps than hBN. I surmise from this that hBN tends to stay around in the rifle bore where the others may tend to break down under heat and/or humidity.

 

[CPorter]

For me the main reason is decreased barrel wear. The side benefits are easier & less frequent cleaning. I started off with moly then transitioned to tungsten disulfide & finally boron nitride.

My girlfriends 6.5-284 has over 1000 rounds through it and the barrel is just beginning to fire check. My .243 has over 2500 and is still going strong.
.

 

[STP]

I`ve used MS2 for the last 3 years. I have been able to go an entire season of F-Class competition with no cleaning and no loss of accuracy. I use bore foam cleaners when we are done for the year and pick up right where I left off for the next year. This includes rifles in .308Win, .260Rem., .223Rem, and 6BRX.