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Old September 9, 2014, 03:21 PM   #1
condor bravo
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Moly coated bullets and chamber pitting

For reduced loads for several rifles I use Trail Boss powder and the black molybdenum coated bullets (as well as standard lead bullets). Two rifles using the MCB’s are Rem Mdl 700 .458 Win Mags and one developed pitting in the chamber (but not in the barrel itself) that eventually became so bad that case extraction was extremely difficult (upon firing, brass would imbed itself in the pits) and required a barrel replacement. Pitting occurred in the forward half of the chamber at about the 1:30 position.

The pitting might suggest rusting but there was no indication of any rust whatsoever, anywhere. The rifle was always stored in an upright position and was never exposed to any excessive moisture. The pitting did not develop overnight but became worse and worse during several months of shooting.

Question 1:
I had read somewhere that moly does attract moisture. Those of you who have used MCB’s, what are your opinion and knowledge of them--favorable, unfavorable, or just neutral?

Question 2:
I’m assuming, or hoping at least, that the pitting (and rusting if any) was not due to the moly coats. Has anyone out there experienced anything similar, and/or knows how this pitting might have occurred?
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Old September 9, 2014, 03:54 PM   #2
243winxb
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Quote:
read somewhere that moly does attract moisture.
I read it traps moisture under it, causing rust. I remember seeing a barrel sectioned online showing it.
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Old September 9, 2014, 04:34 PM   #3
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When moly coating was developed and patented by the late Roger Johnston who owned NECO, it took about five minutes for Wheeler Engineering to ignore the patent and put out their own kit. When NECO called them on it, the owner responded that he was an attorney and could afford to keep them tied up in court for so long it would drain their coffers, so they gave up on enforcing the patent with kit makers, (though they do license it to Norma and Sierra gets theirs coated by a licensee, as I understand it; they look like it).

The result was that everyone and his brother got into the game of provided bullet moly-coating kits that used one method or another. Most did not use NECO's methodology exactly, and more important, they did not copy NECO's materials list. Where NECO uses a laboratory grade, high purity, acid-neutralized moly. Most if not all the others use much less expensive technical grades of moly that can have a lot of free sulfur in it. The sulfur reacts with air and moisture to form sulfurous acid radicals (SO3ˉ) radical and that activates the surface for oxidation. I also read somewhere that the cheapest moly used was recycled from metal stamping operations and that it also contained some free iron, which would make matters worse, but I have not verified that independently.

Finally, when the moly process first came out, it decreased metal fouling so well, that some competitors also concluded that it meant they could go all season without cleaning their guns. Add that long, uninterrupted exposure to moly with free sulfur in it, and it's not surprising that pitting was discovered.

As far as I'm concerned, NECO's moly is the only one I'll let my bores be exposed to. The other moly product I have confidence in is Sprinco's Plate+ Silver, which uses sub-micronized acid-neutralized moly that puts a coating in the bore. Regular cleaning is needed. I recommend Boretech's moly cleaning solvent.
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Old September 9, 2014, 06:46 PM   #4
condor bravo
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Looks like I can get the Bore Tech moly solvent from Midway. Thanks for the info. Curious, using the Hawkeye, that there was no pitting in the barrel, just a section in the chamber.
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Old September 9, 2014, 07:01 PM   #5
jmorris
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What bullets are you using?

Are you using moly powder?

How are you applying it?
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Old September 9, 2014, 07:27 PM   #6
condor bravo
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I should have made that clearer to begin with. These are commercially prepared lead bullets under the name Bear Creek Supply so don't know their moly application procedure or what moly formula is used.
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Old September 9, 2014, 08:47 PM   #7
condor bravo
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Note that Bear Creek Supply, located in Calif, seems to have a very good reputation. All bullets I guess are molys and they seem to have more handgun bullets than rifle. What I use mostly are 360 gr RNs for .458s and .45/70s.
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Old September 10, 2014, 09:07 AM   #8
jmorris
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Molybdenum only on lead bullets gives awful results.

Most of the "coated" bullets only have a small percent moly in them but I have no idea what they actually use.
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Old September 10, 2014, 04:33 PM   #9
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Quote:
Molybdenum only on lead bullets gives awful results.
One of the best loads I ever had for my XD 9mm was Billy Bullets 115gr moly coated over some Universal (charge weight escapes me at the moment). That gun absolutely loved that load - and all Billy Bullets are cast lead moly coated.

I've coated some .223 projectiles with the Lyman moly. Not sure what grade it is, and haven't actually loaded or shot any of them yet. Mostly did it as an experiment (worked very well, BTW on the process). Having the dry moly powder to use as a dry lube on some things is also nice.
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Old September 10, 2014, 07:49 PM   #10
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Too many people use "moly" when they are talking about something else.

If your .223 projectiles are cast or swaged lead (not jacketed) and you try the Lyman kit, that is true molybdenum powder that tumble coats the bullets (no baking/curing needed) you will find the results much less than ideal.

I have the MSDS for one manufactures "moly" bullets, the coating contains less than 10% molybdenum in the mix.
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Old September 11, 2014, 10:43 AM   #11
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Chamber pitting-only could also be a different issue than corrosion. If there is a lumpy build up of moly in the chamber, it is possible for rifle pressures to hammer it against the surface enough to create an indentation, analogous to ringing a chamber. I wish I could see what the pits look like, but you'd need the camera adapter for the Hawkeye to get that.
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Old September 11, 2014, 01:38 PM   #12
condor bravo
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Camera not available. Here's a little more description of the situation. Examination of a fired case showed some 8 to 10 pits around the 1:30 position that are about 1/32 inch in diameter. Bolt lift was fairly easy but chamber extraction almost required a mallet. Hope not to find any more of these ptoblems. Barrel replacement is expensive. Douglas did a great job matching the Rem barrel and within a reasonable length of time.
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Old September 11, 2014, 05:24 PM   #13
condor bravo
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The above might be a bit misleading. The pits, of course, are in the chamber at about the 1:30 chamber position, extending rearward from the mouth about 2/3 the length of the chamber. The fired cases show matching projections as the brass imbeds itself into the pits. The cases iron out of course upon sizing.
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