Randy Robinette (Where did we buy boron?)

[John Kielly]

I thought we used moly, tungsten & boron because they enhanced shooting intervals & maybe because they had an effect on accuracy.

If I'm correct, why is their slipperiness an issue, other than how much powder we ned to load with to do the job?

 

[jim b.]

We’ve been studying boron nitride, tungsten disulfide, and molybdenum disulfide as bullet coatings in order to reduce the friction between the bore and bullet jackets. There has been MUCH discussion over the past few years about the pros and cons, the effects and effectiveness of molybdenum disulfide, which has been under scrutiny the longest. Now 2 other substances enter the discussion – hexagonal boron nitride (hBN) and tungsten disulfide (Danzac or WS2), although Danzac/WS2 has been around for a while.

Stating this a bit simply without getting into details, introducing moly coating of the bore and bullets into a load, without any other changes, reduces this friction between bullet and bore, and results in a slightly lower velocity, but a greater reduction in firing pressure. So, if you add a bit more powder and bring the firing pressure back up to the pressure level of the non-moly load, you’ll get higher velocity. The most slippery substance (the substance with the lowest coefficient of friction – COF) allows for the greatest reduction in firing pressures and/or the greatest velocity increase. That’s why we want to know which substance lubricates the best (most slippery).

It is also said that the bullet is deformed less as it more easily enters the rifling and passes through the bore, resulting in higher ballistic coefficients. It is said that the less violent passage of the bullet through the bore allows more stable bullet flight and allows the bullet to “go to sleep” sooner after it exits the muzzle. Also, many claim that you can fire many more shots before you notice a meaningful decrease of accuracy, and that when the time to clean does come, that the bore cleans faster & more easily.

One more benefit to boron nitride is that it is said to be nonhygroscopic (does not absorb moisture from the atmosphere). One potential problem with molybdenum disulfide is that moly is hygroscopic, so you need to be aware of that when you store your rifles for a while with moly-coated bores.

Now, I really don’t want to get into a debate with anyone over any of the several points above. Much of it has been discussed at length, and different persons will have different opinions. What I’ve written above is a synopsis of much previous discussion by many shooters. All I’m trying to do is comprehensively answer John Kielly’s question about slipperiness.

Jim B.

 

[Donald]

The method I use to coat bullets is with a small hobby type rock tumbler. The rubber drum is about 4" in diameter and about 4" deep. I found a small glass jar (actually a minced garlic jar) that just fits into the rubber drum. It fits in side ways and allows you to just barely get the lid back on the rotating drum. The jar has a lid that has a built in gasket and does not leak. The jar will easily hold 100 bullets, maybe more. I used it to tumble bullets with a dab of moly. No steel shot, just tumble the bullets. After about 2 hours of tumbling they come out looking like factory jobs after you rub the excess moly off. Francis B. was kind enough to send me a small samle of the BN. I just got a different jar that was clean, put about 2 screwdrive tips of BN in the jar along with about 50 bullets and tumbled for about 2 or so hours. Just the bullets and BN. After dumping the bullets out on a towel and swishing them back and forth a few times they seemed to only have a slight frosty look. I could not pick one up by the point. Only by grasping the bullet by the body could you pick it up. Kind of like the old STP commercial years ago in trying to hold the screwdrive dipped in it. From my experience with moly I know the velocity will be lower with a given load. During a match I only shoot necked bullets but I like to play around with stuff like moly and the BN. I just hope the cleaning thing works out as I hate to clean then fire 1-3 fouling shots to condition the barrel. This just seems a waste of bulles and barrel life. I can see that it might even open the use of different powders. Thanks again Francis......Donald.