[gerard488]

About 12 years ago, I used some winchester supreme ammo in my 7mm Rem Mag. they were the nickle plated shells with a black coated bullet. I fired about 12 rounds without cleaning the barrel and had to leave it a day or two.
When I did clean, I looked thorough the barrel and noticed that the rifling grooves were plugged about 6 inches back from the muzzle. Took about 20 minutes with a brass brush to get it cleaned .
About a year later, I saw the exact same thing happen to a 270.
Both rifles were win model 70.
Has anyone else experienced anythng like this?

 

[fourniermod11]

disulfide mobylene=(black coated bullet) disulfide mobylene toxic on air i dont like this bullet , whit muzzle brake maybe is prob for smoke face return...

 

[Bindernut]

Moly-Disulfide is hygroscopic, meaning that it absorbs moisture. The film deposited in the bore sucked up some moisture from the air and held it close to the steel causing the corrosion that you found.

The biggest problem is getting that moly film out of the bore to prevent it from continuing to happen. It is a stinker to clean out since it does bond to the steel very well.

If you shoot moly-coated bullets, treat them like corrosive-primed ammo and clean the rifle as soon as possible afterwards.
Storage in a humidity controlled environment will help too.