Look at what some of the barrel makers say.

From Hart:

.... What about Moly coated bullets?



? We do not recommend the use of moly bullets, as we have not seen an increase in accuracy or barrel life from using them. We have measured moly buildup up to .0005 for the first 2 - 3 inches in a barrel. We have not found a cleaning method that adequately removes the moly without potential damage to the barrel. If you elect to use moly bullets, we recommend that you contact the bullet manufacturer for details on the cleaning method they recommend.




From Kreiger:

: What is our opinion on moly-coated bullets?

A: The jury is still out on this one. For the most part accuracy is a wash between the two. Your gun might shoot better, or it might shoot a little worse. For the most part we feel there is no difference. You will have to try them to find out if your gun "likes" them. Most people agree that you do lose a little velocity with them. As far as barrel life goes, there is no hard proof that a barrel will last longer using moly-coated bullets. These bullets might help a barrel that fouls badly (copper) to shoot better for a longer period of time (number of rounds being fired without cleaning). This could possibly help factory rifle barrels or ones not having a good bore finish

From Lilja:
Q. What is your opinion of the use of moly coated bullets?
A. First, as described in our section on barrel break-in, we do not recommend the use of moly coated bullets for break-in. The break-in process requires the use of an uncoated jacket if it is to be successful.
Secondly, at the risk of offending those that promote the use of moly, we can't see much benefit to it for a couple of reasons. There are two basic claims made for the use of moly, reduced fouling and increased barrel life. We'll look at both of these.

We agree that bullet jacket fouling in a barrel can and will cause accuracy problems in a barrel. But for the most part, jacket fouling in a hand-lapped, match-grade barrel is minimal. For the small amount of copper fouling that does remain in most barrels, conventional cleaning methods can and will stay on top of the fouling. We recommend cleaning solutions like Shooter's Choice and/or GM Top engine cleaner mixed with Kroil oil and the limited use of Sweet's solvent. Our suggestions for cleaning can be found in the Cleaning and Break-in section.

We have examined barrels with our bore scope that have had an excessive amount of moly fouling layered with powder and jacket fouling. The only way we could remove this buildup was through relapping of the barrel. Perhaps part of this type of problem results from a mindset that says "Hey, I'm using moly now and I don't have to clean very often." So if you do elect to use moly coated bullets we recommend that you still clean as often as before.

So, the obvious question to us is, if regular cleaning is still required with moly and if a bullet/cartridge/barrel combination does not foul to any great degree without moly, what is the advantage to moly?
This leads us to the second part of our answer. Some of the promoters of moly claim an increase in barrel life. While this sounds good on the surface we must ask the question: what causes a barrel to shoot out? Barrels wear out, or no longer shoot up to their original performance levels, because of erosion to the throat area of the barrel. This erosion is caused by heat and pressure created by burning powder. As a throat lengthens, velocities fall off and accuracy can suffer too. Eventually more and more of the throat will be eroded and moved forward. Also the diameter of this eroded section will increase. We have seen take-off barrels that had fully 1/2 of the length of the rifling completely eroded.

The key to this type of erosion is that it is caused by hot powder gases under high pressures and not by friction between the bullet and the barrel. We have read a report from a military test that examined this type of barrel wear. It was found that over the course of tens of thousands of rounds the actual groove diameter of the barrel was only increased by a few ten thousandths of an inch. It is this type of wear that moly might prevent or slow down. But in this test the throat area grew progressively longer and larger in diameter from gas erosion, not friction between the bullet and barrel.

So from our point of view, moly coated bullets are not going to prevent the type of throat erosion we have described, that the type of wear caused by friction between the bullet and barrel is insignificant, and that the prevention of jacket fouling through the use of moly is marginal at best and that moly may add another type of fouling to the barrel.
There is one type of shooting that may benefit from the use of moly coated bullets, in our opinion. In an effort to find the "perfect" bullet, target shooters using the 50BMG cartridge have manufactured solid bullets that are lathe-turned from materials like brass, bronze, copper and even soft steel alloys. These bullets can cause a considerable amount of barrel wear caused by friction between the barrel and bullet. The bore and groove diameters of these barrels do increase in diameter as a direct result of this friction. And this wear is not caused by the hot powder gases that will erode a throat in more conventional barrels.
In this case it seems as though, in our testing, that coating bullets with moly will help reduce this type of barrel wear.
We realize that our opinion of moly does not go along with the wisdom and promotions of the day. But we're willing to listen to opposing views if you have one.