Molybdenum disulfide?

[schutzen]

I have no direct knowledge of the suitability of Mo2 or WS2 as a coating for cast boolets, but I do coat my jacketed .224 bullets with Tungsten Disulfide (WS2). On the jacketed bullets, I have seen a slight improvement in the groups. In general, I have not reduced my group sizes significantly. However, on a 5 shot group of WS2 coated bullets 3 of the five shots will touch each other in every group. I have not been able to duplicate this with non coated bullets. Now before everyone asks, yes everything was the same. Same lot of bullets (500 bulk pack, 1/2 coated & 1/2 left naked), all brass from the same lot processed together, all primers from the same brick, and identical powder charges all from the same 8lb jug. My shooting partner has experienced the same results. The cost to coat the bullets yourself is negligible. We have coated all of our .224 bullets for the past 2 years and have been very satisfied with the results. Besides, I need all the help I can get to hit the target.

PS For the purists among us. I shoot jacketed bullets in my .223, but is only because I have been unable to push a PB boolet to 3000 FPS no matter what lube I tried.

[felix]

Excellent, Linstrum! ... felix

[Glen]

c3d4b2 -- You asked me to review the two refrerences you posted, so here are my comments:

1st paper (from 1953) -- in this paper they took a 1/4" layer of MoS2 between two rotating discs (in air) and measured friction as a function of time, and found that friction increased over time, and that addition of water (either liquid water or vapor phase humidity) had an impact on friction. They make one comment about how "the water was observed to be acidic" and yet their apparatus (and the procedure described) has NO method for measuring any kind of pH, or change in pH. They say something about a "stained surface" that looked like it might have been acid etched, but MoS2 is very dark and could have easily impregnated the pores of the steel to create this "stained surface" (after all it had been ground under a 1/4" of the stuff for 6 hours!), or possibly the steel could have undergone a surface sulfidation reaction which would have also discolored the surface. With a 1/4" layer of the stuff in between the discs, the observed change in friction could be due to changes in how the MoS2 was aggregated (something that liquid water/humidity is known to do to powdered ceramics), and that in turn would impact how the MoS2 would be able to lubricate (hence change in friction). As for the "corrosion" they observe, it's hard to comment on that as the photographs are of such poor quality, but I am skeptical of the conclusions because of the primitive nature of the experimental design and execution. Besides, liquid water has been known to corrode metal surfaces for centuries.

Bottom-line: This experiment has virtually nothing to do with how MoS2 would behave in a gun barrel. This experiment was carried out under oxidizing conditions, with a 1/4" of MoS2, with liquid water, and their conclusions are based on a visual discoloration of the metal surface. If I had been asked to review this manuscript for a peer-reveiwed technical journal (something I do on a regular basis for journals in the areas of chemistry and nanomaterials), I would recommend to the editor that this paper only be considered after major revision, and additional experimental work, because the conclusions are not adequately supported by the experimental observations.

As for the second paper (the Soviet journal from 1960) -- I'm not sure I got everything straight from that one because it's kind of hard to read, but they were studying the corrosion effects of MoS2 in electrochemical reactions, specifically anodic corrosion (once again oxidizing conditions), implying that there was an applied potential on the metal surface. There are no experimental details given in this abstract, only conclusions, so it's hard to really comment substantively, but one clarification that I can offer is that the comment you cited about the "SO2 chamber" refers to studies that were carried out in a chamber containing SO2 in the atmosphere, intentionally added for accelerated aging studies, it did NOT come from the MoS2.

We have MUCH better tools for studying surface chemistry today than they did back in 1953 or 1960. The question I have to ask is, "If this MoS2 corrosion is a real phenomenon, with the widespread use of MoS2 industrially, why haven't other folks used these newer, better tools to study this problem?".

I stand by my opinion that MoS2 is safe to use in gun barrels and in bullet lube, and I will continue to do so (and no, I do not have any commercial interest in any products involving MoS2).

[c3d4b2]

Glen,

Thanks for the clarifications.

[XWrench3]

well, my $0.02 worth on moly is this. it makes wonderful bullet lube, and a fine dry firearm lubricant as well. i have used it on many things from motorcycle chains, to assembly lube (cams, rockers, final drive gears, etc.), to spray bullet lube (lyman) which i have also used for dry lubing my ccw semi-auto loaders. i have never had a bad experience with it yet, except in one case, and that was the manufacturers fault, telling me to use it on crankshaft main bearings (automobile style plain bearings) that was a mess! but anyway. in any other application i have used it in, it shines!

[runfiverun]

one of the things i have noticed about the moly is the way it holds heat.
i have wondered if it pulls heat away from the boolit/bbl as it moves along and soaks it up.
i know as i am mixing it in the b-wax and it is hot it will stay that way for an extremely long time and i have to keep mixing and mixing. it will keep the mix hot for a long time in the lubrisizer too i can warm it up and run about 4-500 boolits through the star and the lube will still be soft on the boolits for quite a long time till it cools dow.

[leftiye]

I've seen it here before, but can't remember the percentage that was recommended. Members were saying to use the moly sparingly when adding it to lubes. Does anyone remember what the percentage that was recommended was?