chamber finish...just how smooth ?

M

mike in co

Guest
ok i'm still new at chambering, and two of my last chambers have extraction issues.....
so just how smooth? do you polish to a certain grit ?
inquiring minds want to know


thanks
mike in co
 
alinwa said:
The question of whether or not a polished chamber holds the brass from sliding MORE or LESS than say a 240 grit finish is not easy to answer, there has been much long and convoluted discussion on the subject.

It is currently my belief that the most slippery surface (lowest slippage coefficient) between brass and steel occurs with the steel polished to around 320grit.

As always, others' opinions will vary.

As always, these opinions will be based on various experiences.
Click to expand...
Might help.
 
Some polish a bit, some don't at all. A good reamer requires none or very little polishing.
 
Unless you have rings in your chamber from a chip welding itself to your reamer, your extraction issues may be the result of something else.

To answer your question. I "polish" a chamber with 320 emery soaked in Kroil at 500rpm. I'm not really polishing. I'm putting a cross hatch on the chamber walls. The idea is so that the case "bites" the chamber when its fired to help reduce the brass from flowing.

Some say this is not needed, but it's never hurt anything so I stick with it and I like the "honed" appearance of the chamber afterward. It's just a few strokes so I'm not really changing dimensions all that much. (if at all)

Just something to think about.

C
 
mike in co said:
ok i'm still new at chambering, and two of my last chambers have extraction issues.....
so just how smooth? do you polish to a certain grit ?
inquiring minds want to know


thanks
mike in co
Click to expand...


Mike, yours is a question that comes up often and there is much disagreement as to whether or not polishing is even necessary. A good reamer and good workmanship leaves a nice finish in the chamber that requires no polishing. If it makes you feel better and you just feel like you have to "burnish/polish" use 320 grit on a split dowel and make a few light passes with plenty of lube. I use WD-40 and turn the lathe about 1800 rpm.

As far as the cases "gripping the chamber", I don't think it makes a bit of difference whether you burnish or not but there is another very important consideration in some situations; the Beggs chambers are a classic example, let me explain.:rolleyes:

Early Beggs chamber reamers cut a .4400 diameter .200 from the bolt face. The Lapua 220 Russian case as it comes from the box measures .4400 or sometimes a tenth or two less. The Hornady sizing die for the Beggs cartridges measures .4400 at the aft end. After the chamber is reamed to depth, polish the aft end with 320 grit on a split dowel to .4420. After three or four firings with full charges, cases come out of the gun measuring about .4415 at the pressure ring. This gives the Hornady die something to size and everything is all well and good; extraction is effortless and cases last almost forever.

In the future, Beggs reamers should be ground to .4420, .200 in front of the bolt face, which will eliminate the need to polish the finished chamber.

Hope this helps. If you have any questions, please contact me at

genebeggs@cableone.net

Later,

Gene Beggs
 
Scotch Bright finish, wrapped around a small dowel makes a nice cross-hatch without really removing anything.
 
I do a quick polish or more like Chad to make a cross hatch pattern on the chamber with 320 grit sandpaper. As long as you don't get carried away, you won't change dimensions little if any. I haven't seen it cause a problem, but it could help with sticky extraction.
 
ive always been happy with the chamber as cut with a sharp finish reamer. of course i dont do the quantity some of the others do.
 
ok, one of the two chambers is an ar15/223. i did polish a little a couple of days ago and was able to shoot it today.

not good. failure to eject about 90%. this is most likely the gunsmiths fault( that would be me). the fired brass shows bright spots in a ring 270 degrees on the neck, bright ring 360 just at the start of the body past the shoulder, and a slight mark 360 up .42 from the base of the case. the base mark looks like a burr(it is very fine, cannot feel), but the neck shoulder stuff i do not know. i'm sending the reamer back for inspection( there is the possibilty i damaged it).

next up is the 6beggs.....

( again remember i'm new at this)

mike in co
 
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