Reaming Dies with chamber reamer

Discussion in 'Reloading' started by birdiemc, Jan 14, 2020 at 8:29 PM.


Help Support Long Range Hunting by donating:


  1. birdiemc

    birdiemc Well-Known Member

    Messages:
    653
    Joined:
    Jan 1, 2011
    I've been reading on the interwebs about reaming custom dies. Most folks say that using the chamber reamer to make a sizing die does not work but then I came across Newlon Precision where they say that their dies are used with the same reamer used to cut the chamber. So what is the correct answer?

    Another thing lots of folks say online is that most commercial reloading dies are made on a CNC lathe, which makes me wonder with the chamber isn't cut the same way?!?!
     
  2. pttp

    pttp Well-Known Member

    Messages:
    48
    Joined:
    Oct 11, 2017
    It is the bullet seater die, not the sizing die, that is cut with the chamber reamer. Wilson makes blank dies for this. Threaded bullet seater dies can also be modified this way.
     
    L.Sherm likes this.
  3. birdiemc

    birdiemc Well-Known Member

    Messages:
    653
    Joined:
    Jan 1, 2011
    That's what I read in several forums, but that company I posted a link to says you can use their die blanks with a chamber reamer (includes sizing dies, micrometer seating dies, body & forming dies, and seating dies)
     
  4. BountyHunter

    BountyHunter Well-Known Member

    Messages:
    5,219
    Joined:
    Jun 13, 2007
    You can use it, it just will not size the brass
     
  5. J E Custom

    J E Custom Well-Known Member

    Messages:
    9,668
    Joined:
    Jul 29, 2004

    There are two different reamers for chambers and dies.

    One is called a chamber reamer and is cut to a SAMMI or custom dimensions.

    The other is called a sizing reamer and is cut to a size that allows the dies to size the case to fit the chamber and allow for spring back.

    If you want to make your own dies It is best to have the reamer maker make your chamber reamer and also make a matching sizing reamer.

    I would use caution when reaming some dies because some are flame hardened and will ruin that expensive reamer, You can buy die blanks that are not heat treated or hardened and wont hurt the reamer. It is a total blank except for the caliber hole through it to guide the reamer pilot.

    If you use the same reamer for both the chamber and the die, the die will be shorter and will not fully size the case at the web. and the neck diameter will not sized correctly unless you build a bushing die with replaceable bushings.

    J E CUSTOM
     
  6. birdiemc

    birdiemc Well-Known Member

    Messages:
    653
    Joined:
    Jan 1, 2011
    JE, curious what is the difference in size between the 2 reamers? Sounds like you probably have some of your own and might be able to shed some light, I check PTG to try and see if they have information online but couldn't find anything.

    Looking at a few SAAMI drawing it looks like ~ .0005 clearance between the case and the chamber for the most part(.001 difference in diameters for .0005 clearance all the way around) so it makes sense that the same reamer would result in a die that is larger than it needs to be to size the brass back down to proper dimension. However it seems this would only be a problem in new brass. In my little brain it seems fire formed brass wouldn't need the case to be sized at the web. If I understand what's going on inside the sizing die, the only time that portion of the die would come into play it seems would be when bumping the shoulder back. During that process the case length from shoulder to base is being shortened which would cause the OD to want to get larger, so the ID of the die determines to what extent it can grow. In this instance the sizing die is preventing the case OD from getting bigger rather than sizing it down to a smaller OD. So I think it would stand to reason that a die the exact same size as the chamber would result in a more appropriately sized case body if in fact my thinking is correct and the die is preventing the case from growing as opposed to squeezing it to a smaller dimension.
    Now this all goes out the window with any brass that is not fire formed, because if the brass is too large and needs to be sized to a smaller OD, then having a die ID the same size would result in brass not fitting into the chamber because of spring back.
    If I'm thinking correctly:
    1. (Not fire formed)oversized brass being squeezed to a smaller OD springs back to a larger OD than the ID of the die.
    2.(Fire formed) Undersized brass while bumping the shoulder back would be expanding to a larger OD, until contacting the die, then would spring back to a smaller OD than the ID of the die. Resulting in a case to chamber clearance equivalent to the "spring back dimension"
     
  7. birdiemc

    birdiemc Well-Known Member

    Messages:
    653
    Joined:
    Jan 1, 2011
    Holy moly I'm a long winded s o b
     
  8. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,954
    Joined:
    Aug 10, 2003
    My reamer sets include rough chamber, finish chamber, and sizing. I get go/no-go gauges with the order, and I have the barrel finisher cut me a widget for shoulder bump measuring, chamber end clearance setting, turned neck clearance, and seating land relationships (with finish chamber reamer, from barrel end cut off).
    I set all parameters of my reamers (I fill out blank prints), and my final formed cases exactly match my plan for dimensions, clearances and capacities.

    I've had my barrel finishers chamber Wilson seating die blanks for me. Apparently this is an easy affair(for a seating die), having received no concerns about it.
    For sizing, I have not seen my where my sizing die maker(JLC Precision) has actually used my sizing reamers(even while sent with dies and reamer print).
    Somehow a custom die maker can set correct dimensions-without my reamers. I don't know how, but he's done a great job, so I can live with the mystery so far.

    Also, a barrel finisher may not actually use the rough chamber reamer. Many of them drill the rough chamber, and use only the finish reamer.
    Given my experience with this, it's understandable to me how many get by with a finish chamber reamer only.
    You can send a custom sizing die maker fired brass in the form you want properly sized, and they do their stuff. The right stuff.

    I highly recommend reloaders, building guns, to fill out a reamer print and order their own. It's cheap, and it gives you important control over the outcome.
    I also recommend having sizing dies matched for fully fire formed cases.
    You just can't go wrong with this.
     
  9. J E Custom

    J E Custom Well-Known Member

    Messages:
    9,668
    Joined:
    Jul 29, 2004

    First, I would contact Manson precision reamers and ask them. I did not question them about the difference because they made the chamber reamers and based the sizing reamers off the chamber reamers.

    As you know reamers are very hard to measure unless you cut a false chamber with it checking as you go so I depending on their expertise. I use the reamers and they do a great job.

    I am curious about the difference but it may vary based on the cartridge picked.

    The sizing reamer Has to be smaller to size properly but how much larger itis I couldn't tell you.

    I bought the die blanks from PT&G But prefer reamers from Manson and JGS.

    J E CUSTOM
     
    MNbogboy likes this.
  10. Edd

    Edd Well-Known Member

    Messages:
    3,605
    Joined:
    Jan 26, 2011
    Here are the prints to a couple of my reamers.........
     

    Attached Files:

    MNbogboy likes this.
  11. birdiemc

    birdiemc Well-Known Member

    Messages:
    653
    Joined:
    Jan 1, 2011
    Thanks for that Edd, that is much better information than what I was able to find floating around the internet. That neck size difference is interesting .0079. If neck wall thickness is .014 (what I measured on several prepped cases) that would make the ID of the neck while it is inside the die .260 resulting in .004 neck tension, but that disregards spring back after the case leaves the die. How does that number compare with what you're seeing? This is all fascinating to me.
     
    MNbogboy likes this.
  12. J E Custom

    J E Custom Well-Known Member

    Messages:
    9,668
    Joined:
    Jul 29, 2004
    I looked for my reamer drawings but have not located them to look for differences But thanks to Edd you have something to go buy.

    The main point it to use a GOOD reamer maker and have him make it the same time that he does the chamber reamer so the CNC process can be changed only in the areas that need to be saving any set up error.

    Spring back should/can be dealt with, with the dies, and/or neck turning and annealing because the reamer cant adjust for case hardness due to firing.

    The other option is to use the sizing reamer for the body and shoulder and then machine the neck chamber to except bushings to make the neck tension adjustable
    and then chose the bushing you need. I have done this for dies that use the same case with different caliber bushings for different bullet diameters. (Tricky, but it can be done).

    J E CUSTOM