I posted about this once before over here. But then photobucket went and broke the Internet, making that post less useful. So since someone asked about it the other day, I thought I'd try to post a condensed (maybe) version.

I had run a few thousand commercially coated 9mm through a Bowers VERS-9s. This was a mix of 124 and 147 gr. bullets. What I found was I get a buildup in the can as bad as or worse than shooting bare (lubed) lead. The cone of crud building up around the aperture in the blast baffle had restricted the opening to the point a bullet could not fit through without rubbing hard. I'm guessing I wasn't too far from doing some serious damage to the can.

Here's what the blast baffle looked like:



I had only been crimping enough to take out the flare in the case mouth. And no, I hadn't been shaving bullets as they seated. The barrel was a surplus Uzi SMG barrel, and had gotten pretty dirty. So I didn't know if the bore crud was scraping coating as the bullet pushed through the barrel.

So I scrubbed the barrel spotless and did an experiment. One suggestion had been that the bullets need to fit the bore pretty closely to keep from leaving the coating behind. In slugging a few barrels, I found most of my 9mm barrels were on the generous side. It turns out I had been shooting .356" bullets through a .3575" barrel. So I wanted to try some side-by-side testing with those bullets, and then with something that fit more closely to the bore.  

I didn't want to crud up a pair of silencers (although I almost used it as an excuse to get another one).  Instead, I used a Bowers muzzle brake.  It's made from the same aluminum tubing, and uses the same mounts and end caps as the silencers.  Starting with two new end caps, I ran 400 rounds of the .356" bullets through one, weighing the endcap before and after.  I then put a new endcap on and ran 400 rounds through that one (I scrubbed the barrel clean between tests too).  I was able to find some .358" bullets for this one.  Ammo was shot primarily in short bursts.  No big mag dumps.  

Here's what the brake looks like:



The end result was the .356" bullets left 2.5 times more residue on the endcap than the .358" bullets did.  I thought that was pretty good!  



A comment on the buildup: it was pretty hard, and not all that easy to remove.  I ended up soaking it in solvent for a while, then scrubbing with a copper scouring pad.  I found it much more difficult to remove than lead/carbon buildup would have been on a similar surface.  

Here's a closer look at the stuff on the endcaps.  Keep in mind, this is after only 400 rounds:



Not content to leave things at that, I thought I'd try the same experiment using some fully plated bullets.  I have a bunch of Berry's 147 gr. bullets that mic out at .3555".  So these would be "undersized" for my barrel as well.  The results after 400 rounds was that I only picked up only 2.2 gr. buildup.  The coated .358" bullets gave me 8x more, and the .356" bullets a whopping 18x more!

Before:


After:


Endcap:



So after all of this, I still like and shoot poly-coated bullets.  They are an economical alternative to plated or jacketed, and can be pushed harder than bare lead.  I just don't shoot them through my suppressors any more than I do bare lead.  

One other comment: Please don't misinterpret this to mean that one brand of bullets is "bad", and the other "good".  Rather, one brand of bullets was not a good fit for my particular barrel.  I still have a few thousand of these, and they shoot very well with little to no buildup in the barrel.  And I intend to order more when I'm out.  I'll just continue using jacketed or plated for my quiet shooting.

A few people have posted that putting baffles in wet tumbler cleans them up. Purpose of removable baffles is to be able to remove to clean. I wouldnt get hung up on it. You should see the inside of my 22 suppressor.

P.S. photobucket stinks.

Awesome post, OP! Thx.

The question that comes to mind is:

-what solvent works best on polymer fouling?  

Rather than the copper/carbon solvent you tried, I wonder if any of the following would work?

-acetone?

-MEK?

Maybe even the weird old "Balistol" water-soluable stuff?

Thanks again.

I guess that's what surprised me about all of this. The barrel stays clean, like when shooting a jacketed bullet. But once the bullet "uncorks" from the barrel, it's a different story.

I wonder if the coating gets cooked as the gasses blast past the bullet once it exits the rifling. But if that were the case, you would think you should get some sign of burning on the bullet base too.


I had seen this issue with a commercial poly coated bullet I tried 10 or 15 years ago. I don't recal brand name, or if they listed a specific type of coating they used. Running .45s through the Reising, I found I was getting a noticeable buildup in the comp. I think I may still have several hundred of those somewhere.

As for cleaning, I think I'll just stick to using poly coated bullets in non-suppressed applications. I would have to think about them for use in compensated barrels. At that point, some type of solvent would likely come in handy.

Never seen polymer buildup in barrel but if you get it, I would try a shotgun wad cleaner. No doubt it has acetone or something like that in it.

Something to keep in mind:

A lot of commercially coated bullets are coated with a polyurethane based coating, IE paint.
Most home casters/coaters use a dry powder (shake and bake) that is a polyester based product.

IMHO:
The paint coating is faster to do.
The dry powder coating is superior to the paint coating.

Polyurethane coating is less forgiving/hard.
Polyester coating is soft/pliable.

The red bullets which caused the buildup use Hi-Tek coating.  I don't do any casting / coating. I just buy the pre-coated commercial stuff. But it seems this is the most common / popular product for the DIY coating crowd.  I'm not sure about what was used on the blue bullets.

What is the makeup of the Hi-Tek coating, and does this agree with what you posted?

Just trying to understand here.

Excellent and important point!

As DryFlash points out: not all "coatings" are the same.  

And "polymer" simply means "plastic" - without further definition; there are thousands of plastics and an near infinite number of chemical combinations which might make up a coating.

One example:  the commercial "black bullet" uses (or once used) molybdenum mixed into the polymer coating.  Moly is a controversial coating for bullets.  

The powder coating DryFlash uses does not contain moly.  And it initially clings to the lead using static electricity, then is thermally fused (melted together) to form a very, very tough coating!  

Still others use the "Hy Tech" coating out of Australia. And in Europe, reloaders were using actual latex house paint as a coating (not sure if they still do).

Hi-tek coating is a hard paint/polyurethane. It uses a a/b formula, a being the coating & b being the catalyst. The end result is a hard urethane/epoxy coating.

Your blue bullets (bayou bullets) use the same thing. The hi-tek coating pictured above is sold by bayou bullets.

The dry powder coating that most home casters/shake and bake coaters use is a dry powder that is held on the bullets by shaking the bullets in a #5 (recycle #) plastic tub with the bullets/powder/hard plastic airsoft bb's. This creates static electricity when the bowl with the bullets/powder/bb's are shaken and the powder sticks to the bullets. If you look up the msds safety sheet for the dry powder coatings you will see them listed as a polyester powder coating.

They both use heat to make the final product. The big difference is the dry powder coating is melting/liquifying from the heat and it flows/smooths out to a smooth soft polyester coating. The hi-tek coating uses the heat to kick the catalyst off and to evaporate the liquid carriers of the pigment.

1 coating is hard, the other is more pliable/soft. The soft coating is more forgiving and will bump up easier to fill/obturate/fix bbl issues.

A hard alloyed bullet with a hard coating is a bad combo when trying to get a bullet to obturate in an oversized bbl. A bullet with a soft alloy and a soft coating will easily bump up to fill oversized bbl's along with bbl's with imperfections.

A taurus pt111 g2, taurus is known for their oversized bbl's. A soft bullet 8bhn/9bhn with a dry powder coating sized to .356". The taurus bbl slugged out at .358". A hot load with a home cast/coated 125gr hp.

No tumbling, leading, nothing but performance.

I cast all my 9mm bullets with 8bhn/9bhn alloy, then coat them with a dry polyester coating and size them to .358". That way I can use any 35cal bullet I cast in the 9mm's/38spl's/357's. A 1911 chambered in 9mm after a 500 round range session with the .358"/soft alloy/pc'd bullets.


A close-up of the bbl after 500 rounds with a 25,000psi+ load.


1 wet patch (hoppe's #9) and 1 dry patch later ='s a clean bbl. No brushes/leading/fouling/nothing/nada.


I haven't shot a lot of these coated bullets in cans, just a couple 100 in a 308. I have shot countless 1000's of them in firearms with muzzle breaks and ported bbl's. There's never been any leading/fouling in any of them that I get with the traditional cast/lubed lead bullets.

With any lead bullet (coated or otherwise), fit is king. But in the coated bullet world a soft alloy is queen. Soft bullets and soft coating solve a lot of issues that happen with the hard alloy bullets with the hard coatings.

Hopefully you work everything out. I was just trying to point out that not all coated bullets are equal and not all coatings are equal. I just found it odd that no one brought this up until now.

Thanks! Lots of good info here. When I started on this, I realized I was only playing with a couple of variables, and not doing an exhaustive set.

The bullet hardness is something to consider, especially when buying from commercial casters. Traditional lead bullets are typically cast as hard as possible. I would expect most commercial casters will keep their alloy / hardness the same to simplify inventory.  They would use the same stock of bullets for lubing or for coating. I don't know of any current casters who use "hard" lead for lubed bullets and "soft" lead for coated.

It's less an issue for 9mm machine gun blasting ammo. I'm currently still working through a bunch of Berry's seconds that I bought for a lower cost than I can find poly coated bullets. But I can't expect to find that type of deal on a regular basis, and I like to have options.

I think that this is a coating problem more than a size problem.   I have had bad leading in my barrels using SNS Hi-Tek coated bullets, while the Blue Bullets will actually scrub the bore.

I am getting away from coated bullets all together and moving back to plated and FMJ or JHP.    

I do still have quite a few Blue Bullets 115gr left that I want to try loading as 9Major for my open gun at a velocity around 1550fps just to see how the coating holds up and whether my comp leads up.   The SNS bullets were completely unsuited to that use as I could see silver in the ports in my comp in as little as 10 rounds, even though they were loaded to minor power factor with Power Pistol.