Molybdenum Disulfide, a compound that reduces friction, can be used to coat bullets. This coating offers many benefits, such as reduced barrel heat and the ability to fire longer string of shots between bore cleanings. Reduced friction can reduce internal barrel pressures. This means that coated bullets may run slower than uncoated bullets, even if the charges are equal. Shooters who use coated bullets may be tempted to “bump-up” the load to restore velocity, but you must be careful. Be careful when increasing loads for coated bulletsWe warn shooters to not immediately increase the charge weight when you first use coated bullets. You may need to shoot a few coated rounds before you start to notice the pressure reduction. Some guys automatically add a grain to the recommended “naked bullet charge weights” when they shoot coated rounds. This is a dangerous undertaking. For the first dozen coated cartridges through a brand new barrel, we recommend using “naked” loads. Use a chronograph to monitor velocity. It may take 30 rounds to see a 30-50 fps reduction in velocity, which indicates that the anti-friction coat is fully effective. Recently, a friend of ours was testing moly-coated bullets 6mm in a 6-6.5×47. Moly was never used before in the barrel. Our friend added a grain of moly to his “naked bullet load” thinking that it would compensate for the lower pressures predicted. He found that his loads were initially WAY too hot. It took him 30+ moly coated rounds to go through the bore for his velocity to drop. This was a sign that pressure had dropped due the moly. The pressures were too high for the rounds fired prior to that point, and he had to throw away some expensive Lapua brass because the primer pockets expanded excessively. Lesson: Start low with coated bullets. Do not increase your charge weights over naked bullet loads until you can clearly demonstrate that the pressure has been reduced and the velocity has decreased. After barrel cleaning, follow the steps below.
If you use Moly and clean your barrel aggressively after the match, you might want to shoot 12 coated “foulers”, before you start your record fire. Robert Whitley who has used Moly for some of his rifles tells us that he likes to shoot 10-15 coated rounds before starting a record string. You won’t see the full benefits of moly in a “squeaky clean” bore. Read our Guide to Coating Bullets to learn more about dry lubricants. This article covers the three most common bullet coatings, including Molybdenum Disulfide(Moly), Tungsten Disulfide(WS2 or “Danzac”), and Hexagonal Boron Nitride(HBN). The article discusses pros and cons for the different bullet coatings, and provides step-by-step illustrated instructions on how you can coat your bullets with a tumbler.
