Piston cup rusting?

[Juanaranda2558]

So I’m new to the forum , but I just bought my wolf a1 upper and shot about 300 rounds and I took out the piston to clean it and saw that the piston cup had a bunch of oxidation is this normal ??

[apex]

If you don't oil steel, it may rust especially if you're in a very humid part of the country/world.
I recommend a wipedown with Ballistol at least once/month to all the steel parts during the summer months. That said, is it actually rust or is it oxidized copper residue? Also what ammo are you running? I've found that different ammunition manufacturers use different grades of copper in their jackets. Particularly, Barnaul's lacquered 55gr FMJ line seems to have a copper jacket that is extremely prone to oxidization- 100 rounds into a testfire of my (then) virgin 12.5 with only Barnaul and the piston was blue! Ran it through my DI AR to make sure it was the ammo, and the muzzle device was all blue on the inside (this was in 88 degree heat and 84% humidity mind you). Meanwhile, Norma, Wolf Poly/Mil-Classic, 205th-manufactured Wolf Gold, and Prvi 55gr all don't seem to have this issue or at least not to the extent Barnaul lacquered does.
Oddest thing is a majority of Wolf Poly is manufactured by Barnaul

There's also the (small) possibility the ammunition you're running has poorly-made primers and are leaving salt residue.

[Kalakar]

So I’m new to the forum , but I just bought my wolf a1 upper and shot about 300 rounds and I took out the piston to clean it and saw that the piston cup had a bunch of oxidation is this normal ??

Following Apex's post, if you're able to share some more information, we might be able to help narrow this one down:

1. What ammo did you use?
2. When was the gun last cleaned?
3. What was used to clean it?
4. What weather has it seen?
5. Could you share some pictures?

[Juanaranda2558]

So I used Hoppes #9 on the piston cup and it turned the Hoppes solution blue so I guess it’s just copper residue but it’s hard to clean off and it’s inside the gas port any solutions to cleaning it off and out ?? What do you use?

[Juanaranda2558]

Also I’ve been shooting brassed case ammo from federal

[apex]

So I used Hoppes #9 on the piston cup and it turned the Hoppes solution blue so I guess it’s just copper residue but it’s hard to clean off and it’s inside the gas port any solutions to cleaning it off and out ?? What do you use?

I usually just dunk the pistonhead straight into the Hoppes copper solution bottle for about 5 seconds, let it air out for about 10-20 seconds, then clean it off and wipe it down with a Ballistol rag. For cleaning the carbon buildup out, I use the T91 cleaning kit to scrape it off followed by a brass brush. It gets a good amount of it off with about 5 minutes of effort, could probably get it back to like-new condition if you really wanted to.
https://store.t91tactical.com/T91-Gas-P ... -p87905865

Don't forget to clean out your bore, muzzle device, gas port, gas block, and piston retainer (the black metal part that the piston cup goes inside, and the piston sleeve locks into). Pipe cleaners from your local dollar store or arts+crafts store will do the trick, just dunk one end in the Hoppes and clean it out with the other end and follow it up with some oil.