Chamber polishing

C

chuck furniss

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What is the best method for polishing a chamber that is showing radial tool marks on the brass?
This is causing hard extraction in a minimum size chamber.

Chuck.
 
I am by no means an expert Chuck.

At the moment I am doing a bit of lapping work on some home made swage dies. For your purpose I can recommend diamond paste as an effective lapping compond.

Maybe a brass lap loaded with 2500 grit to start ?

Mike
 
chuck furniss said:
What is the best method for polishing a chamber that is showing radial tool marks on the brass?
This is causing hard extraction in a minimum size chamber.

Chuck.
Click to expand...
For something like a PPC diameter case start with a 1/4" diameter wooden dowel then saw split it about 1/2". Start with some about 180-220 wet-or-dry abrasive. Cut a piece of abrasive about 1" X 1/2" and wrap it around the dowel (I'm assuming here the barrel is chucked in a lathe). Trying to polish a chamber without rotating it in a lathe can give disastrous results!!

Polish till you get the size and finish you want...you do not want a super polished finish, gives too much bolt thrust.
 
Make yourself up a split mandrel out of 1/4" dowel or smaller for a smaller case. Slit the end for a 4-6" long 1-2" wide strip of sandpaper. Slide a strip of paper about a half inch to an inch beyond the end of the slit and wrap the paper around the dowel overlapping itself around the dowel. Wrap in the direction that will keep the paper wrapped up and abrasive side out while the chamber is spinning in the lathe. As the paper wears just tear off the worn end. Google split mandrel for pictures. I have brass and steel split mandrels for use in die grinders as well.

Just to clarify: I do not use the mandrels in a die grinder for polishing chambers. I just mentioned them as they are useful tooling to have around for cleaning up or polishing holes in general.
 
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JerrySharrett said:
You do not want a super polished finish, gives too much bolt thrust.
Click to expand...

Actualy Jerry thats not realy correct and is a bit of an old wifes tale. The chamber pressure is applied to the rear inside face of the brass case. The soft brass case is no match for 60,000 PSI and will stretch easily, so 99% of the load will be transfered to the bolt head regardless of how much the brass "Grips" the chamber..

Cheers
Leeroy
 
Leeroy said:
Actualy Jerry thats not realy correct and is a bit of an old wifes tale. The chamber pressure is applied to the rear inside face of the brass case. The soft brass case is no match for 60,000 PSI and will stretch easily, so 99% of the load will be transfered to the bolt head regardless of how much the brass "Grips" the chamber..

Cheers
Leeroy
Click to expand...

What he said...

I have polished many of my chambers to a mirror finish with 1,000 grit "Wet or Dry" and oil, and there has never been a problem.

Funny about how this wives tale goes - I have heard it both ways, "Never polish a chamber, it'll cause the brass to stick to the walls", and "Never polish a chamber, it'll cause the brass to slip and hit the bolt"

It makes no difference - the "Blish effect" causes the brass to stick to the chamber wall (momentarily) and then release, no matter how smooth it is... unless there is oil on the case or chamber walls.

During that "sticky moment", the case will stretch back at the web, into any headspace there is.
 
'Splain why brass fired in a chamber that has excessive headspace, and the primer will back out? If it is slamming against the boltface, the primer would be flat.
 
Wayne Shaw said:
'Splain why brass fired in a chamber that has excessive headspace, and the primer will back out? If it is slamming against the boltface, the primer would be flat.
Click to expand...

My thoughts - If the primer backs out and does not flatten that is an indication of cartridge head gap or possibly headspace and relatively low pressure. If the primer had flattened that would be an indication of cartridge heap gap or possibly headspace and enough pressure to stretch the brass back until supported by the bolt face. Excessive headspace is measured using steel gauges made to exact specifications, not fired brass. The term headspace and cartridge head gap is commonly misused very often but they are different.
 
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The idea of rough chambers gripping cases better evolved at a time when the 6 BR made its appearance. Neck sizing was way more
common then and tight cases landed on us like a tidal wave. Action work was not all that common either so added together and
given the larger internal surface of the case head the BR cases got us in trouble. True actions and bolt faces along with FL dies
have brought that back to earth. Somewhere in the equation it was believed that one could minimalize this with a rough chamber.
We are talking about a very small piece of time here, but the thinner brass at the forward part of the case expands first and the rear
end grows radially and in length afterwards. Should pressure be low enough, there is little or no growth in diameter or length. Once the
pressure is hiked beyond the elastic limits of the brass, you have tight cases. Leaving solvent or case lube in the chamber brings on
case growth earlier on the pressure curve, it has nowhere to go. Hardened steel plates do have less friction under pressure, but that
situation is not duplicated when using disimiliar materials like unhardened steel and brass.
 
Dennis, I understand how headspace is measured. My point was, the brass obviously grips to a certain degree to cause the primer to back out under those circumstances.
 
the actions at the low power of a primer is not the same as the actions of a full powder load......likely less than 1000psi with a primer and no bullet/wad vs 60,000 psi with a bullet and powder.
cannot compare the two
there is some case grip in a fullpower load which reduces boltface load. does polishing or not SIGNIFICANTLY change the out come...no idea, but reducing the amount of case surface area will reduce the grip, and increase bolt face load.......esp at the top end.....an issue with full loads in short mag cases and ssmag cases ???

mike in co
 
This is purely anecdotal, but on my 6PPC'S, where I shoot at over 60,000 psi on a regular basis, if I leave the chamber "as reamed", the bolt lift and extraction is no problem at all. If I polish the chamber, the bolt can often be tight on the upstroke.

So, long time ago, I decided to leave them 'as reamed'. As for the OP's originol inquiry, if the rings are significant, you will end up with a chamber that could be as much as .002 oversized when you finally get them all out, depending on how deep they are. Try to avoid this in the future.
 
Wayne Shaw said:
My point was, the brass obviously grips to a certain degree to cause the primer to back out under those circumstances.
Click to expand...

The primer backs out from it's own ignition before pressure develops from the powder...

The firing pin drives the case as far forward in the chamber as it can, the primer at this points backs out as far as it can... then when the pressure builds up the case will either slide back or in most cases stretch back or a combination of both.
 
right and when no powder...the primer tends to stick out.....

mike in co
 
I don't believe there's ever been a tool mark deep enough to hang up a case but polishing the chamber out WILL help your problem! :)

Because it'll make the chamber larger.

Polish it out a couple more thou and the problem will disappear.

al
 
I'll guarantee that you are wrong Al. I did one myself several years ago that had a .005 groove. The only way to fix it is to cut off the breech end and rechamber. I have seen a few of those in my time. I will not try to polish .005.
Butch
 
Butch Lambert said:
I'll guarantee that you are wrong Al. I did one myself several years ago that had a .005 groove. The only way to fix it is to cut off the breech end and rechamber. I have seen a few of those in my time. I will not try to polish .005.
Butch
Click to expand...

That's a deep ring :)

But did you shoot it?

al
 
Well Butch, ya got me. I was wrong, there ARE tooling marks deep enough to limit extraction. You've shown me that a 5 thou groove WILL bugger extraction. I'd never pictured a trench this large getting out of any shop.

That said I've had many chambers with rings, rings which show up on the fired brass and get shiny when resizing. But I've never had a ring so large it hangs up extraction!

And I STILL believe OP's problem is a too-small chamber

:)

al
 
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