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Thread: Precise fitting of case to chamber

  1. #1
    Boolit Mold
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    Precise fitting of case to chamber

    Yesterday, I posed a question on the method to cut 45-90 cases to fit my 45-70 rifle. Several responses were received, to which I have chosen a method. My question today is what length would be best to first trim to. My chamber measures 2.114 inches and I plan to mostly shoot paper patched loads. What effect will fireforming and resizing have on the cartridge OAL. My experience with pp loads is to have the case dimension best matched to the chamber length. Most of my Starline cases have never been loaded, but some have been shot and resized in the 45-90.

  2. #2
    Boolit Master
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    Quote Originally Posted by Stoneke View Post
    Yesterday, I posed a question on the method to cut 45-90 cases to fit my 45-70 rifle. Several responses were received, to which I have chosen a method. My question today is what length would be best to first trim to. My chamber measures 2.114 inches and I plan to mostly shoot paper patched loads. What effect will fireforming and resizing have on the cartridge OAL. My experience with pp loads is to have the case dimension best matched to the chamber length. Most of my Starline cases have never been loaded, but some have been shot and resized in the 45-90.
    You will likely get a lot of advice to do a chamber cast -- not knocking that at all - I was not set up to do that so I belled the neck of an overlength case and chambered it - shorten a whisker - repeat and rinse until we got a case that was just neat length without curling the end of the neck in - used that for a reference to trim the others.

  3. #3
    Boolit Grand Master

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    I believe you stated your chamber is 2.114 length in the other post. Most recommend -.010 from that finished. I you can start at that rimmed and fire form a few to see what they do as far as shrink then figure from there. Keep in mind you need some room the mouth dosnt wedge in and not release the bullet. I wouldn't recommend less than .005 clearance though.

  4. #4
    Boolit Master Lead pot's Avatar
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    Cutting down cases like from the .45-90 to .45-70 can be a hit or miss. New cases for say .45-70 are usually short for the chamber.
    When you cut down the .45-90 you could be working with a case that is undersized in the diameter for your chamber and if you cut it right at your chamber dimensions and fire the case it will be short because it will stretch filling the chamber width and this will shorten the length.
    When I use basic brass, like the .45 Norma basic or .45-120/3-1/4" for the .45-2.6 I will cut it 1/10 th" long and anneal the case mouth put some powder in the case that will leave enough room to put a 1/16" cork wad and a .023 card over the powder and fill the case with wax, about 1/4" and shoot just a wax wad. This is enough to expand the case to fit the chamber and also the short over length you will see the transition of the chamber end leading into the throat.
    Then I will trim that case .005" short of the transition. I want my fired unsized case 5 thousands short of the chamber end because when you fire a round with a bullet it will get pulled forward and retract again.
    If the fired case has a slight roll in it was pulled up the 45 common chamber end now days, and this is not good for accuracy.
    When you get your cases fitting the chamber make a record of the length from the front of the rim to case mouth so you can set your trimmer for future trimming the brass because it will stretch again after several firings.

    I know that this is a lot of work but I do this and a few other things prepping cases so I get a consistent bullet release for accuracy.
    But if only shooting 100 yards I have fired .45-70 cases in the .45-90 chamber and knocked over bowling pins.

  5. #5
    Boolit Master semtav's Avatar
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    Quote Originally Posted by Lead pot View Post


    If the fired case has a slight roll in it was pulled up the 45 common chamber end now days, and this is not good for accuracy.


  6. #6
    Boolit Master Lead pot's Avatar
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    Quote Originally Posted by semtav View Post

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BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
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LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
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