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Rust/Pitting in JM Pro Gas Piston Bore

NorCal707

.22LR
Any of you also experiencing Rust/Pitting in the Gas Piston Bore on your 930 series shotguns? Nice of Mossberg to cheap out and not chrome the bore for the gas piston. I guess if one is anal and cleans their gun after every shooting session, it might be less of a problem. Other than that, what do you guys do to keep the problem at bay? I can get the surface rust off using a Scotchbrite pad but there's some pitting that's not going to go away.
 
The 930 is a great gun & well worth the money that Mossberg wants for it. If you have not heard of ( OR3GUN ) research them & their products that they offer for your 930 they are great & can be helpful is disbursing the condensation that your gun makes. If the rust is already gotten to the stage of pitting their might not be a lot you can do about it. This autoloader really requires a good cleaning & ( lube ) after every outing. But with that said it will last a lifetime if taken care of properly. I'am sure other folks will chime in shortly & give you some pro's & con's. Welcome to the forums & good luck with your shotgun.
 
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I have been utilizing a MST from OR3GUN and it really doesn't seem to do much. I live about 75 miles north of San Francisco and the climate here is not excessively wet. I think the only effective solution is stripping/cleaning after every shooting session and lubricating the Piston Bore with a very light coat of Corrosion-X or CLP to prevent further damage.
 
The clean & lube especially of the piston bore is critical to performance. You might need a new one if it is badly pitted. I've watched a lot of video on these shotguns and I use Safariland break free with CLP it's a cleaner / lubricant & preservative for all guns. After I apply this I wipe it back down with a good cloth & then my gun grease is Outers. It say's it is a heavy duty universal lubricant for firearms & choke tube threads. Both of these can be had at Wal-Mart. Your piston bore should pull out easily if it does not take a scotchbrite pad & give it a good cleaning & it's mating insert also. I watch a video once from OR3GUN & was amazed at how much condensation this gun produces from heating up & cooling down. You are correct about cleaning after every use. GOOD LUCK
 
If it's pitted then there's not much you can do. I'm one of those guys that is anal about cleaning my weapons. I guess the military made me that way. A gun is a close tolerance machine tool and must be maintain after shooting or what you are experiencing will happen. Some weapons are more susceptible to moisture than others and the 930 is one of them. I've actually seen some slow motion video on YouTube showing the 930 being fired with the handguard removed. There is moisture flying everywhere. I clean my guns everytime I shoot. No matter if I fire one round or thousand. I prefer Ballistol when cleaning and preserving my 930 JM. When your done cleaning and wipe it off it leaves enough lubricant behind for protection. Kinda like a cast iron frying pan if you know what I mean. I wouldn't use it as a lube for long term storage but for normal use it works great. I quite sure there are many others that work as well or maybe even better but this is my preference.
 
Any of you also experiencing Rust/Pitting in the Gas Piston Bore on your 930 series shotguns? Nice of Mossberg to cheap out and not chrome the bore for the gas piston. I guess if one is anal and cleans their gun after every shooting session, it might be less of a problem. Other than that, what do you guys do to keep the problem at bay? I can get the surface rust off using a Scotchbrite pad but there's some pitting that's not going to go away.
The JM Pro pistons are nickle boron (NiBo) coated, and should be silver-gray in appearance. If yours is blued, call Mossberg, and have the correct part sent to you. NiBo is harder and more wear-resistant than hard chrome, btw.

Without seeing your piston, its hard to say for sure, but I would suspect you have really hard carbon deposits, versus pitting. An overnight soak in a penetrating oil, followed by a rinse off with brake cleaner, generally gets rid of all traces of carbon.

If you have actual rust pitting, that would lead me to believe you did a lot of shooting in a cool area with salt in the air(coastal), or went shooting in a coastal area and put the gun in the car with a/c really running.
 
Rob72 may be on to something. It may only be hardened carbon deposits and not pitting.
I had an experience cleaning an old Remington Model 11, made in 1916 and was apparently cleaned very little. I had to use a dental pick set to clean the hardened carbon off off the internal receiver parts. Soaking them in acetone did nothing. Good news was under the carbon deposits there was no pitting.
 
Mu SBE Precision pistons are stainless steel. They make cleaning them much easier. As far as corrosion inside the cylinder itself it depends on the ammo, and weather. Some of that stuff is plastic and carbon that has attracted moisture. Even though you can get 2,000 shells between cleanings with this piston, and the OR3GUN components if you are in very humid areas, or store your shotgun in humid areas you can clean more often.

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