HBN: A Dry Lubricant for Rifle Barrels
Hexagonal boron nitride (HBN) is a ceramic that has all of the advantages of graphite as a lubricant with none of the disadvantages. HBN is able to withstand temperatures up to 3,300-degrees F under normal atmospheric conditions before sublimation. It will not conduct electricity, become magnetic or attract sand and metallic particles.
It would be nice if we could fabricate rifle barrels out of this material, given its extreme hardness under compression. Unfortunately, it has a weak tensile strength. Any monolithic barrel fabricated from ceramic would shatter like glass from internal or tensile pressures. However, when applied as a coating to the bore of conventional steel barrels, we can obtain the benefits of ceramics without the disadvantages.
Because of its high thermal conductivity, HBN is commonly used as a releasing agent in molding processes involving molten metals and slags. It is also combined in container material for molten metals, non-lead glass and metal oxides. HBN coatings have proven to be excellent in braze stop-off, as well as beneficial for weld spatter release.
A semi-retired engineer from Los Alamos National Lab, Noel Calkins, determined that properly applied HBN will function as a lubricant and outperform all other lubricants (wet or dry), including graphite and molybdenum disulfide. There is no liquid to run out or dry out when applied to rifle barrels or bullets. It reduces wear and increases the muzzle velocity by friction reduction. Sound like a pie-in-the-sky? Well, it isn't!
From a crystallography standpoint, HBN is a hexagonal material that is platelet-like in structure (like graphite). However, it maintains its lubricating properties under greater temperatures, even in a vacuum. For these reasons, it has been referred to as the "white graphite."
When HBN, as a dry fine particulate ceramic, consisting of 0.5 to 14 micron sized particles is burnished into a metal's surface, it produces the effect of a dry lubricant. With this in mind, Noel developed a patented process whereby he could apply HBN to bullets and gun barrels. When the bullet is fired, the particles are small enough that they literally embed themselves into the barrel's bore grain boundaries.
Testing at a national laboratory confirmed that the HBN does, in fact, penetrate into the pores of the steel and produce a long-lasting lubricating effect. How long no one really knows for sure, due to the many variables, but independent testing with an AR-15 indicates no significant reduction in the ceramic coating after firing 4,500 rounds.
It requires 15 to 20 rounds of coated bullets to achieve the desired level of ceramic coating in a bore. After the coated rounds are fired, higher muzzle velocities are achieved, averaging 2% to 5% in centerfire rifles, indicating a better seal and/or less friction. In either case, the barrel stays cleaner, as with less friction there is less tendency for powder residue or bullet metal to stick in the barrel. This is a real benefit for shooters.
We became interested in using HBN to determine if it would be useful for muzzleloader hunters, by reducing or eliminating the need to swab between shots. With this in mind we coated 15 belted bullets with the ceramic and headed to the range. After firing the HBN treated bullets through Jim's CVA Optima V2 rifle, we began our testing.
We used the following black powder substitutes: MZ, Triple7 and Blackhorn 209 loose powders, plus Triple7 and White Hots pellets. We shot various combinations using 260 grain Harvester Scorpion PT Gold bullets with Crush Rib Sabots, 270 grain Harvester Saber Tooth belted bullets and the 250 grain CVA Aerolite belted bullets. The only way to describe the results are: WOW!
Everyone knows if you shoot Blackhorn 209 bore swabbing is unnecessary. However, if you are among the muzzleloaders who use other black powder substitutes, you have to swab between shots. Perhaps not on the second shot (if you have an open bore), but certainly every shot thereafter. With the ceramic treated barrel, we fired twenty rounds without swabbing, using the previously mentioned propellants. While the ceramic did not completely prevent the buildup of crud in front of the breech plug, it was substantially reduced, making it easy to properly seat the bullets.
Since not everyone shoots belted bullets, we coated 20 of Harvester's Crush Rib Sabots with HBN and fired them with Scorpion PT Gold bullets through Mary's CVA Accura V2 rifle. Once again, after firing the treated sabot/bullet combinations, we were able to shoot all of the above propellants without swabbing. Whether you shoot belted or saboted bullets, the HBN ceramic is easy to apply.
For muzzleloaders, the benefits to having a ceramic treated bore are:
We found a general increase in muzzle velocity similar to that obtained by the National Laboratories in centerfire rifles. However, there were significant variances in the muzzle velocities for the powders we tested. One powder did not result in any increase in muzzle velocity, while the others produced increases ranging from 5% to 15%. Each shooter will have to determine the velocity for their own bullet/powder/load combination.
The primary benefits of HBN for muzzleloaders is no swabbing between shots and easy cleanup. We do not want to muddy the water, so to speak, by dwelling on the issue of velocity. Given that a one-time ceramic treatment lasted for more than 4,500 rounds in an AR-15, we believe that a single treatment in a muzzleloader will likely last a lifetime of hunting.
If you think an HBN treatment of your barrel would be worthwhile, you can order an aerosol can of White Silk Diamond from ZYP Coatings. The price is about $40. One can contains enough material to treat about two hundred bullets, enough to coat the barrels of several rifles.
Copyright 2015, 2016 by Dr. Jim Clary. All rights reserved.