Whatever Happened to Moly Coated Bullets?
With the onset of "Social Distancing", I've had more inside time and I've been doing a lot more reading. I've been going through a big stack of Precision Shooting magazines from 96, 97, and 98 so far.
Nearly every issue had an article about the benefits of moly coated bullets. Some issues had several articles. All of them singing the praises of moly coating, or detailing how to produce the best coated bullets. (Rather like the recent adoption of powder coated cast bullets, but even more articles.)
Molybdenum Disulfide is a very black finely powdered compound that has very interesting lubricating qualities. It is biologically inert and nontoxic. It has one of the highest resistances to extreme pressure while still maintaining it's lubricity. The lubricating qualities are phenomenal in protecting against sliding (shear) forces but much less so against rolling forces. That means moly is much more useful in preventing two surfaces from galling or wearing, than it is for protecting bearings, especially roller bearings. Moly particles tend to become imbedded in the surfaces of the bearings with the result that they become less smooth and wear faster.
But back in the mid 90's, moly was thought to be a remarkable discovery as a bullet lubricant. Also, it was said to prolong barrel life, delay barrel erosion, eliminate the need for barrel cleaning, and increase barrel accuracy. It was supposed to do everything short of eliminating wind drift--although come testing suggest that moly would act to effectively increase a bullet's ballistic coefficient and thus maintain a higher down range velocity. The vast majority of long range and precision shooters--bench rest, high power, Palma, etc) adopted moly coating for their bullets. Most of the best known and most respected shooters lauded the benefits of moly and set records using it. Bullet manufacturers offered their products pre coated, and even a few ammunition makers produced cartridges with moly coated bullets.
Then, twenty years later, almost no one is using it. Why? What changed? Why has moly fallen out of favor?
That's not to say that using moly coated bullets had no disadvantages. But they seemed minor compared to the benefits. Moly was black and stained fingers. Unless care was used during the coating process, the moly powder seemed to get everywhere. The moly coating process for bullets was a bit cumbersome. Moly coated barrels were uniformly black inside and after being shot with moly bullets, cleaning patches came out with black streaks forever afterward. And if moly contaminated metal surfaces that should not be lubricated, it was very difficult to remove.
I got to thinking about this after working on my 7x57mm Mauser. I've had this since the early 90's and I used a lot of moly bullets in it at the time. One load using Rel 19 and moly coated 165 gr Nosler partitions was safe and accurate in my rifle at up to 3000 fps.
Moly coated bullets have less friction through a rifle barrel than do uncoated bullets, and typically have lower velocities with the same load of powder. They need about 4-6% additional powder to recover that velocity difference. Even so, it is though that the pressures generated in the chamber and barrel are lower with moly coated bullets (even with the additional powder) than with uncoated bullets.
It occurred to me that my loads with the moly coated 165 gr Noslers may not be safe with uncoated bullets. It seems I will have to continue using coated bullets, or start from scratch and work up new loads.
Anyway, why did the moly coated bullets fall out of favor?