Educational Zone #99 – Moly Coating Rifle Bullets

Many years ago, shortly after WWI, US military rifle competition shooters complained about copper fouling when shooting long strings of shots in rifle matches. The bullets used were jacketed metal bullets, with a copper alloy as an exterior covering. When fired at velocities greater than about 2,500 fps, the friction caused the copper to be deposited on the bore of the rifle.

Cast lead bullets had been used in the past, and it was found that adding a groove to hold some bullet lubrication, usually a mixture of oils and wax, would greatly reduce fouling in the bore. But it was assumed that jacketed bullets would not have a problem with fouling.

It was true that the fouling was much less than with lead, but there were still problems with deposits of jacket metal in the bores of rifles. A good cleaning could remove almost all of this fouling, but it wasn’t practicable to clean the bores during competition.

It was theorized that maybe some kind of lubrication might increase the time between cleanings. So, some bright soul decided to just dip the first ¼ inch of his loaded military Ball cartridge into a jar of grease. As the bullet was shot, the grease was spun off and coated the bore, and seemed to help with the fouling.

But, as is often the case, someone began to think, “If a little is good, a lot ought to be better”. So, some guys got all sloppy and started cramming their cartridges into the grease cans before loading them, but they stuck them in too deeply and got grease all the way down onto the cartridge case. If you know much about internal ballistics, you can imagine what greasing the cartridge cases did to the situation.

Cartridge cases expand upon firing and the brass case swells up and grips the sides of the chamber, sealing the chamber from any back blast of burning propellant. The grease on the cases kept the cases from gripping the chamber and allowed them to cause excessive back pressure and even caused some actions to fail.

The Army solved this problem by outlawing the use of grease as a bullet lubricant and everyone just went back to cleaning their bores between strings.

Fast forward to a couple of decades ago…..

Some bright guy got the idea of lubricating jacketed bullets with a dry lubricant. They tried several types and settled on molybdenum-disulfide, or moly for short. Moly is a very black, very slick compound. By impregnating a copper jacketed bullet with a moly coating, it will lubricate the bullet and reduce the friction as the bullet goes down the bore at high velocity, thereby reducing copper build-up in the bore. This allows long strings of shots between cleaning without any reduction in accuracy. And, as an added bonus, when you do clean the bore, it cleans much easier, as there is less fouling.

I started moly coating some of my rifle bullets many years ago.

To do this, you need some equipment.

Specifically, you need a vibrator/tumbler and some moly powder.

I have a Tumbler that I bought from Midway that I have especially for moly coating bullets.

The only thing that is mandatory is that you must have a top that seals the tumbler, as if the top has holes in it, like my Lyman tumbler does, you will get dust all over the garage.

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I also have a container of Moly that is made for this application.

It is a small 8 oz, can, but I have been using it for years, and haven’t even put a dent in it, as it only takes a very small amount.

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Today I am going to be moly coating some Sierra Matchkings, that are .311 caliber, 174 gr BTHP bullets.

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If you have used the tumbler before, it will already be coated with the moly and all you have to do is dump the bullets into the tumbler…

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And add just a very little moly powder. I use just the amount that will fit on a screw driver blade.

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Then screw on the lid and plug it in.

A word of warning: This is about the loudest noise you will ever hear from a tumbler.

Since there is no polishing media in the tumbler, the bullets are just bouncing on the bottom of the container and it makes a lot of noise.

I start it up and let it run for about 20 minutes.

The bullets bounce around in the moly and it impregnates the surface of the bullets.

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When you open the tumbler, the bullets will look like this.

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I built a box to use to separate the bullets from the excess moly.

Continued below...

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It consists of a box to catch the excess powder, and an upper box with a 1/4 inch screen to allow the excess powder to fall through, leaving the bullets on the screen.

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I then pour the contents of the tumbler onto the screen….

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And let the powder fall through.

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I then dump the bullets into the original container and they are ready to load.

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Here’s what the bullet looks like, before and after.

How do they shoot?

Well, some shooters suggest that moly coated bullets are more accurate.

This may be true, but maybe it is just that the reduction in barrel fouling is where the improvements come from.

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I do know for a fact that it is much easier to clean up a barrel after shooting moly coated bullets.

The first patch will come out black from the moly, but there will be much less copper fouling to worry about.

Is moly coating for everyone? I don’t think so.

But if you shoot as much as I do, you may find that it is worthwhile.

Now let’s go to the range with those bullets loaded up to shot in my old rifle.

The rifle is a 1917 Enfield in .30-06.

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It is a beautiful rifle.

But the barrel is very worn and it shoots .308 caliber bullets into “patterns”, not groups.

So, I bought some Sierra 175 grain .311 BTHP bullets and moly coated them.

Then I loaded them up and that’s what we shot today.

Here’s the first target, at 50 yards.

The top group is some 150 grain .311 bullets over some AA-4350.

The bottom group is five shots of the 175 grain bullets over some AA-4350.

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Take a closer look at that bottom group.

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Then, this is the last 5 shot group of the day. 

How’s that for a 93 year old rifle with a poor bore?

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Conclusion:
It is fun to shoot an accurate rifle.

3 Comments on Educational Zone #99 – Moly Coating Rifle Bullets

  1. Potatos Browning // January 28, 2016 at 1:54 am // Reply

    Very interesting. I’m glad you got good accuracy back into your old rifle. It seems that slightly oversize bullets work well in the worn bore. However, the more interesting comparison would be shooting the .311 bullets without moly and comparing the results to the same bullets with moly.

    Thanks for your test.

    Potatos

  2. rangerrick // May 10, 2016 at 10:59 pm // Reply

    I too have used moly bullets for years in every thing from my ar 15 , 22-250, to my 7mm magnum. Thing I found odd is it does improve accuracy, but above 30 caliber it doesnt seem to work in 375 h&h, or 35 whelan, or 45-70. I seem to think the larger calibers need the drag to spin the heavier bullets

  3. Unfortunately moly powder inevitably gets everywhere and sticks to everything it touches and is near impossible to completely clean up.

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