blackened necks?

[Al8095]

Hey guys, I had a quick question about my fired cases I've saved. I shoot a 7mm ultra mag and have about 100 cases saved from Remington factory ammo. I just got a book to learn from, it talks about blackened necks due to insufficient pressure or too much chamber space. I looked for cracks but can't see any. I couldn't really catch what it was saying but it said they would only be good for a few more loadings. The whole neck is pretty black, is that not normal after shooting? Could someone please clarify this for me?

 

[Sako7STW]

Is the brass itself discolored or is it residue from the powder? Mine has some on it as well but a lil scrubb and shiny again. I dont see how that would ruin your brass.

 

[JR]

What could be of help, sometimes what happens is the neck portion of your chamber is oversized...when the round is fired, the neck of the brass expands to the chamber, so if you have an oversized neck at the chamber, you will get less of a gas seal, hence possible insufficient pressures, and the blowback discolours the neck..Watch for case stretch, watch for thickness of the necks of your brass after firing...

Guy at work here had a similar problem with his 6.5 x 284, which we pinpointed to neck was oversized on the reamer(was an old reamer) than according to current Norma prints, was getting black necks, cracked necks, holes in necks, after 2 or three reloads..We ordered a reamer to Norma specs, rechambered barrel, and that problem disappeared with it..

JR

 

[Al8095]

Yeah, it is definitely residue that comes off with some scrubbing. There are no defined cracks or anything that I can see. JR, are you talking about major outside diameter growth or neck wall thickness? I have just ordered a micrometer so I can't take any measurements yet. It is a factory rifle so it wouldn't suprise me if the neck chamber was oversized.