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For a given load you will notice a reduction in muzzle velocity of a few percent when moving to moly coated bullets and moly coated bore. In my non-moly'd 3000 FPS .223 loads moly reduces my muzzle velocity by about 100 FPS (3.3%).
This is a real physical effect. The moly is really doing something. In that sense, it is NOT snake oil. The question is, what is it doing and is it a good thing?
What the moly is doing is reducing the static and dynamic coefficients of friction between bullet and barrel. Great words, but what do they mean? The static coefficient of friction is a measure of how hard it is to START something moving, and the dynamic coefficient of friction is a measure of how hard it is to KEEP something moving.
If you plot barrel pressure versus bullet position in the barrel, or plot barrel pressure versus time, the area under the pressure curve (which ends when the bullet exits the muzzle) is directly related to the muzzle velocity for that barrel and that bullet. Since for a given load moly reduces muzzle velocity it must be affecting the pressure curve in some way. Again, this is a real effect.
Since the muzzle velocity is lower the area under the pressure curve must be smaller. Since the bullet versus barrel position curves (non-moly and moly) have the same length (the length of the barrel), and knowing that moly in other applications is a lubricant, it is safe, though not precise, to assume that the moly is reducing the height of the curve and thereby reducing peak pressure.
In my humble (?) opinion there is a correct way to use moly, and my guess is that most people are NOT using it correctly. Cleaning your bore then shooting 100 moly-coated bullets is the WRONG way to coat your bore. Doing it this way will embed fouling and copper under the moly-coat which makes your moly-coating patchy, inconsistent, and adhere poorly to the bore. The embedded fouling may also absorb moisture and lead to the barrel damage some have reported. Smearing moly randomly down the bore with moly-coated bullets is a poor technique.
The goal is to get an even, complete, metal-bonded moly coated bore. To do this you must coat the BORE. Check out my page on Moly Coating a Rifle Bore.
This is on another page, but it bears repeating, MOLY IS NOT A PROTECTORANT. Moly is a dry lubricant. You still need to protect your bore with your usual protectorant. I oil the bore with BreakFree CLP. I juice it up real well, then run a patch down it before shooting, then shoot a few fouling shots.
Now you can shoot moly or non-moly bullets. If you shoot moly'd bullets the bore coat will last indefinitely. You may want to renew it periodically depending on the rifle's use. For benchrest, shooting only moly'd bullets, I renew the coat every 500 rounds. During a typical 3 hour shooting session I will fire up to 50 rounds. Shooting non-moly'd bullets I'd renew it more often. I do not use moly in my "tactical" rifles, only in my precision rifles.
I will not make any claims for performance enhancement, but will simply report that I am getting less than 1/2 MOA performance out of a run-of-the-mill AR-15, and I am not a particularly good shooter. With load development I took the rifle from 2 MOA with military ammo to an occasional 1/3 MOA with handloads and moly. These are 5, 5-round groups. One claim that I will make is ease of cleaning. When shooting moly'd bullets from a moly'd bore, a few patches of MP-7 followed by a few patches of CLP and I'm done. Sometimes for grins I'll run a NYLON brush down the bore once or twice after the MP-7 and before the CLP. I must note that some state that nylon is more abrasive than brass. They point to the wear on the ferrules of fishing rods. This is a poor rational as we do not have brass fishing line with which to compare the ferrule wear.
What do I think that the moly is doing? I think that it is providing more consistent friction coefficients leading to more consistent performance. The only evidence that I can offer is comparative muzzle velocities for similar loads with and without moly.
Rifle is a 20" stainless barrel AR-15.
Bullets are 52 grain Sierra HPBT Matchkings.
Each standard deviation is based on a 10 or 15 round sample.
Powder is Accurate AA2200.
All powder was dropped by a Dillon 650 using the same powder drop.
| With Moly | Without Moly | |||||
| Powder | Muzzle FPS | Muzzle StD | Powder | Muzzle FPS | Muzzle StD | |
| 24.5 g | 2995 | 29.2 (40F) | 22.5 | 2921 | 41.9 (60F) | |
| 24.5 g | 2983 | 9.7 (20F) | 23.0 g | 3015 | 35.0 (60F) | |
| 24.5 g | 3076 | 15.5 (52F) | 23.5 g | 3035 | 34.4 (60F) | |
| 25.0 g | 3113 | 24.3 (40F) | 24.0 g | 3137 | 24.7 (60F) | |
| 25.0 g | 3182 | 21.9 (40F) | 24.5 g | 3183 | 47.2 (60F) |
Note that all the non-moly were shot in the summer and the moly'd was shot at various times in the year. The ammunition was always at the ambient temperature.