Technical Newsletter From Your Ballistic TechniciansVolume 6, Issue 1
(This article was written by David Tubb, president and owner of Moly Coatings, Inc., the company that is moly coating Sierra bullets. The methods and procedures utilized by Mr. Tubb are his own for barrel treatment with moly-coated bullets. The opinions reflected herein do not necessarily reflect the opinions of Sierra Bullets. However, we have been asked the question often enough that we feel compelled to offer one possible answer.)
One of the first questions I'm asked by shooters new to using moly coated bullets is, "How do you clean the gun?" This article will address that question, as well as answer another accompanying question: "How often do you clean the gun?" I am assuming this is the first time you have used Sierra Moly Coated Bullets in your firearm. It is very important to get all the residual copper jacket fouling out of a barrel before starting with moly bullets.
Sierra bullets are coated by Moly Coatings Inc. (MCI) using the NECO process. Other coating processes and/or providers may yield vastly different results following these cleaning methods. To do that, you'll need a specialized cleaner like Sweet's 7.62 Solvent. I use a one caliber oversize brass brush (7mm brush for a 6.5mm bore, for instance). I liberally drench the brush with Sweet's every other time it exits the muzzle. I have brushed some barrels 60-plus strokes in order to remove the fouling. Finish with 2-3 patches. Now, Sweet's tends to eat up brass brushes; however, my method is considerably faster than letting the cleaner soak, and, I believe, lessens any chance for barrel damage from doing so. Likewise, you may find that using oversized brushes, especially in smaller caliber bores, reduces brush life span. To me it is a small price to pay for greater cleaning efficiency.
By cleaning with this method initially you have emptied the jacket and powder fouling from the stress cracks and tool marks inside the barrel. It will now take a few shots to recondition or re-season the bore -- in other words the rifle probably won't group too well with whichever bullet you feed it (moly coated or not) until it's re-seasoned. The number of shots this takes depends on how many rounds have been through the barrel; it will take more rounds as the barrel becomes more worn. To then clean the barrel after firing Sierra Moly Coated bullets, I use one of two different methods based on the caliber. For "efficient" cartridges such as .308 Winchester, .223, .30-'06, and others where the effect of jacket fouling is normally not as critical as larger, less efficient rounds (7mm STW for example), I use a nylon brush liberally doused with Hoppes #9. I run this brush 15-20 strokes. This method normally results in the first and maybe second shots not going into the group, which is the same thing I would experience using non-coated bullets. Be advised that I am using match grade barrels which are stress relieved and don't have group shifts from barrel heating. On this note: I have found that lightweight factory barrels will usually "walk" (change impact point) as they heat up. These barrels will usually go another one or two rounds before shifting point of impact when using moly coated bullets.
For less efficient cartridges like 7mm Magnum, .257 Weatherby, .264 Winchester Magnum, and others where jacket fouling can affect accuracy in just a few rounds, I again am using Hoppes #9 with a snug fitting brass brush liberally coated with the solvent. It takes 15-20 strokes with an application of solvent each time the brush exits the muzzle end. If you have shot the rifle to the point that it is throwing shots from fouling you may have to repeat the 15-20 strokes with solvent. Again, the first one or two rounds will not be in the group. Following brushing with either method, I use a couple of wet patches to mop out the bore. If you're going to go shoot after cleaning, the barrel is ready as is. If you're going to store the rifle, I recommend running a wet patch through the bore before storing and another before taking the rifle out to shoot.
As for how many rounds, or how many more rounds, I can shoot using moly coated bullets, as an experiment I have run up to 450 through my 6.5mm-08 match rifle without seeing any accuracy deterioration. I find, however, that I am normally cleaning one third less often with moly coated bullets in any of the aforementioned efficient calibers. In the less efficient calibers, it's about half as often: for example, approximately every 50 rounds with a 7mm STW or every 80 with a 300 Winchester Magnum.