why?

[george wilson]

Why do you want a mirror chamber? I understood many years ago that too smooth a reamer caused the cartridge to apply undue pressure to the face of the bolt.

 

[Fitch]

Why do you want a mirror chamber? I understood many years ago that too smooth a reamer caused the cartridge to apply undue pressure to the face of the bolt.

That's true, but it's only part of the story, and not, in my opinion, the important part of the story. The best write up and analysis of chamber finish and it's consequences I've seen is here: http://www.varmintal.com/a243z.htm Highly recommended reading. He also does some experiments on polishing that indicate it's not practically possible to get the chamber too smooth. The best one can do with 600 grit and Flitz appears to be about optimal.

The bottom line: a smooth chamber might increase the bolt load by a thousand pounds (10% to 15%) but it radically decreases (factor of four) effective plastic strain and thus case thinning and the chance of case head separation. Decreased plastic strain also increases case life: number of reloads.

People will do what they want. I oil polish my chambers to a barely visible (with a 10X loop) cross hatch with 1,000 wet & dry wrapped around a small dowel - with the spindle spinning at top speed it doesn't take long. I don't use Flitz because I don't have any. The bolt will take the slight additional load a lot better than the cases will respond to thinning.

I am also very careful to size my brass so I only bump the shoulders by 0.002" max which also helps reduce the plastic strain. I use the Redding Competition Shell Holder Sets and full length resizing dies to do that in a repeatable fashion for my hunting ammo.

Fitch