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Thread: Help needed in ordering a chamber reamer

  1. #16
    Join Date
    Apr 2008
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    Cloudcroft, NM
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    655
    Quote Originally Posted by South_Pender View Post
    I've made some progress in specifying the chamber reamer I'd like to get. I wanted a .265" neck diameter, .030" freebore length (to be able to shoot light BT bullets), and 1.510" overall length. I obtained a standard chamber diagram from one of the reamer makers--this one for a no-turn 6PPC--and made the changes to it shown in red in the picture below. I'm planning to turn necks.

    What I need your advice on is whether these changes I've made are consistent with the rest of the dimensions in the drawing (I'll have the neck diameter at the shoulder changed to .2655, I guess). Should there be other changes given the revisions I've made, or will this chamber work fine?

    Your advice is much appreciated.

    When you changed the OAL from 1.525" to 1.510", you forgot to shorten the neck length to .300". If your base diameter of .442" is .200" from the bolt face, you might want to tighten that dimension to .440". Also make throat diameter .2437" as mentioned by Mike Bryant. Also remember that a .268" - .269" neck diameter (also mentioned above) allows you to still neck turn Lapua brass, or shoot Norma as is. Why not have the best of both worlds?

    I also Just noticed your diameter tolerance. Should be tighter at minus .000" and plus .0004", not plus .001". This is mainly because of the throat diameter needs a tighter tolerance.

    Michael
    Last edited by mturner; 02-23-2019 at 02:01 AM.

  2. #17
    Join Date
    Jan 2015
    Location
    Vancouver
    Posts
    46
    Many thanks to all of you who have contributed here. Below is my final attempt at designing a 6 PPC chamber reamer for my upcoming project. I've incorporated most of the suggestions offered. The one final question I have is whether I can be completely sure that the newer Norma 6 PPC-USA brass will chamber in this design. I know that the newer Norma 6 PPC-USA brass is slightly different dimensionally from the "true" 6 PPC, and I want to be sure it will work in this chamber. Does anyone know offhand whether this brass will work in the chamber below, or where I could find some dimensions for the Norma brass?


  3. #18
    Join Date
    Aug 2018
    Posts
    15
    The shoulder on the Norma brass is set back appx .007 further than my 6ppc chamber. Takes a couple of firings to blow them out. The necks are appx .265. If you need it, I will measure and give you the oal. I am sure it will chamber.

  4. #19
    Join Date
    Jan 2015
    Location
    Vancouver
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    Quote Originally Posted by CCrider View Post
    The shoulder on the Norma brass is set back appx .007 further than my 6ppc chamber. Takes a couple of firings to blow them out. The necks are appx .265. If you need it, I will measure and give you the oal. I am sure it will chamber.
    Thanks, CCrider. That's good information. The .265 you mention must be without any turning. Would you happen to know the diameter at the base (or .200" above the base) and at the shoulder? I'm wondering how much more the chamber at those dimensions should be than the brass to ensure smooth chambering without excessive expanding on firing.

  5. #20
    Join Date
    Aug 2018
    Posts
    15
    .436 at 200
    1.081 base to shoulder

    OAL 1.503-1.507 (I measured several)
    Last edited by CCrider; 02-27-2019 at 06:40 PM.

  6. #21
    Join Date
    Dec 2003
    Location
    washington.........STATE that is.
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    10,278
    Quote Originally Posted by South_Pender View Post
    I'm wondering how much more the chamber at those dimensions should be than the brass to ensure smooth chambering without excessive expanding on firing.
    Please explain what this means?

  7. #22
    Join Date
    Jan 2015
    Location
    Vancouver
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    Quote Originally Posted by alinwa View Post
    Please explain what this means?
    Here's what I meant: If you have an unfired case you plan to use that is, for example, .430" in diameter at the shoulder, how much greater than that should the chamber dimension be at that point to be sure of smooth chambering and sufficient room to expand? Similarly, if the diameter of the unfired case you're planning to use mic's .4372 at a point .20" up from the base, what should the chamber diameter be at that point? .439"? .440"?

    Hope it's clear now....
    Last edited by South_Pender; 02-27-2019 at 07:46 PM.

  8. #23
    Join Date
    Apr 2008
    Location
    Cloudcroft, NM
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    655
    Quote Originally Posted by South_Pender View Post
    Here's what I meant: If you have an unfired case you plan to use that is, for example, .430" in diameter at the shoulder, how much greater than that should the chamber dimension be at that point to be sure of smooth chambering and sufficient room to expand? Similarly, if the diameter of the unfired case you're planning to use mic's .4372 at a point .20" up from the base, what should the chamber diameter be at that point? .439"? .440"?

    Hope it's clear now....
    The dimension at .200" should be between .4395" and .440". If you get it to tight, expect a click on extraction. Also make the inside neck shoulder junction with a .060" radius, not a .075" radius. Keep headspace a 1.075" from boltface to shoulder, just like you already have it.

    Michael
    Last edited by mturner; 02-28-2019 at 01:16 AM.

  9. #24
    Join Date
    Jan 2015
    Location
    Vancouver
    Posts
    46
    Thanks to all of you for your insights and advice.

    I've gone ahead and ordered the reamer from Dave Manson.

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