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Thread: Chamber polishing

  1. #1
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    Chamber polishing

    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.

  2. #2
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    Jul 2011
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    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

  3. #3
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    Quote Originally Posted by chuck furniss View Post
    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.
    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.

  4. #4
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    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.
    Last edited by WSnyder; 08-05-2011 at 01:50 PM.

  5. #5
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    Quote Originally Posted by JerrySharrett View Post
    You do not want a super polished finish, gives too much bolt thrust.
    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

  6. #6
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    Quote Originally Posted by Leeroy View Post
    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
    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.

  7. #7
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    '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.

  8. #8
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    Quote Originally Posted by Wayne Shaw View Post
    '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.
    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.
    Last edited by Dennis Sorensen; 08-02-2011 at 10:41 AM.

  9. #9
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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.

  10. #10
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    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.

  11. #11
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    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

  12. #12
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    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.

  13. #13
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    Quote Originally Posted by Wayne Shaw View Post
    My point was, the brass obviously grips to a certain degree to cause the primer to back out under those circumstances.
    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.

  14. #14
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    +1 on what Jackie said. I'll bet they are too deep to polish.
    Butch

  15. #15
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    right and when no powder...the primer tends to stick out.....

    mike in co

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