hBN - Bullet Coating

[PNWJeeper]

What methods are being used to coat bullets with hBN? Are you simply adding it to tumbling media or simply shaking it onto the bullets.

And has anyone tried applying it to the bore of a barrel?

Curious in Oregon.

[Rick in Oregon]

I'm not using hexagonal boron nitride (hBN), but WS2, as do some others here. My method of coating bullets is an RCBS Sidewinder rotary tumbler and the impact plating method. By using 3/16" steel burnishing balls (roughly equal weight bullets to steel balls) with a pinch of WS2 for 1/2 hour, then run for 5 minutes in another drum lined with newspaper for polishing and removing excess powder, and the bullets emerge bright shiny silver, with almost exactly an even .001" coating; no lumps like moly.

Some here use the same or similar method (vibratory tumbler/glass jars w/balls&bullets) and get the same results, so I'd guess it would work just as well with hBN, can't imagine why not.

As for bore coating, after cleaning a barrel I shoot with WS2, I use denatured alcohol mixed with WS2 on a couple of wet patches, then two dry to remove excess, and shoot coated bullets only in that barrel.

BCB, if you see this, please comment, I'm curious too.

[Bayou City Boy]

All I have ever done for the past ~20 years is coat a clean barrel with colloidal graphite and shoot nothing but naked bullets, even in my 17 caliber rifles.

Colloidal graphite is the only bore treatment I've ever seen that I liked the results you get from doing it. The rest have all seemed like some form of snake oil with down sides to me. But that's just me....

-BCB

[Fred_C_Dobbs]

I've switched from WS2 to hBN but the process is identical. I just degrease the bullets, dry them and put them in the rotary tumbler with the boron powder. If you have a vibrating tumbler, you'll probably need to add BBs or steel shot. I've never used them in my Thumler lapidary tumbler and the results don't seem to suffer for their lack. The coated bullets need a bit of polishing after with either paper towels or a soft cloth or both.

The barrel will coat itself after enough shots but that's not the efficient way to do it. Regardless whether it's moly, WS2 or hBN, if you start with a bare bore, every time you fire a coated bullet, a little of the coating rubs off the bullet and sticks to the barrel. This continues until the bore is coated enough and slick enough that it no longer wipes anything off the bullets. The problem with "shooting it coated" is that your MV and POI will continue to shift from shot #1 until the barrel is fully "conditioned." It's not typical but I saw a post in another forum from a guy shooting a 6.5 Norma with moly bullets and he said it took his barrel a couple hundred rounds to stabilize!!

You can jumpstart the process by one of two methods. The first is to run a patch through the clean bore wetted with Lock-Ease graphite lubricant (liquid, not aerosol). Some non-coated bullet shooters do the same to minimize CBS shift. The other method is to mix the hBN powder with some hi-percentage (90-91%) rubbing (isopropyl) alcohol. Shake it up, soak a patch with it, run it through the bore and let it dry. I've used both and it doesn't seem to make much difference. I have a slight shift in the CBS and my "conditioning" is complete; I'm dead-on from shot #2 onward.

If you shoot nekkid bullets in a fully conditioned barrel, you'll get the same process in reverse until all the coating gets wiped off onto the departing bullets. If you have to switch to un-coated bullets, it's better you should give the bore a good cleaning first.

In case no one has told you, expect to lose a bit of MV with the slicker hBN-coated bullets. In a .204, probably 40-50 fps. But you'll also lose some max chamber pressure, probably close to 2000 psi. Percentage-wise, you'll lose about 5x as much chamber pressure as you do velocity, which gives you opportunity to safely increase the charge. Or you could get used to the reduced MV and you should have a slight increase in barrel life. If you push the coated bullet's Pmax back up to where the original nekkid bullet's load was, you'll have a higher MV but with the same chamber pressure. For the better part, that also means the nekkid bullet's published load data doesn't exactly apply to coated bullets.

[PNWJeeper]

Thanks to all three of you for the response(s). I will try the WS2 in hopes that it expedites the conditioning of my new Savage .204 barrel and lessens the copper fouling cleaning frequency.