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Thread: Measuring Revolver Throat Diameter

  1. #1
    Boolit Buddy
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    Measuring Revolver Throat Diameter

    It was recommended that I check the throat diameter of a revolver, and my calipers won’t fit inside of the frame. Would the proper way to do this be to cast the maybe the first inch of the cylinder end of the barrel with cerro safe? Thank you. Jim

  2. #2
    Boolit Grand Master



    M-Tecs's Avatar
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    Swing the cylinder out on a double action or if a single action remove it. Calipers for this are less than ideal. Pin gages or small hole gages are preferred.
    Last edited by M-Tecs; 05-19-2020 at 11:31 PM.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

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  3. #3
    Boolit Master
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    And lacking a set of pin gauges, tap soft slightly oversize soft lead slugs through the throats and measure the slugs. Do it with the cylinder out of the gun and firmly supported on a non-marring surface.

    Cerrosafing the forcing cone won't really tell you much more than what you can see with a bright light. Barrel groove diameter takes a back seat to throat diameter too. You'll want to size your bullets to fit the throats anyway, and if the forcing cone is rough there's ways to remedy that.

  4. #4
    Boolit Grand Master



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    I believe I misread the post. If you are looking to check for constriction under the barrel threads slugging works better for me than cerro safe.

    If you are looking to improve accuracy or reduce leading read the last to paragraphs in post #7 http://castboolits.gunloads.com/show...35#post4906635
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

    "Before you argue with someone, ask yourself, is that person even mentally mature enough to grasp the concept of different perspectives? Because if not, there’s absolutely no point."
    – Amber Veal

    "The Highest form of ignorance is when your reject something you don't know anything about".
    - Wayne Dyer

  5. #5
    Boolit Buddy
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    Thank you very much for setting me straight. I think I got it, thank you.

  6. #6
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    "Would the proper way to do this be to cast the maybe the first inch of the cylinder end of the barrel with cerro safe?"

    That will do nicely if you remove and measure the cast at the appropriate times as per the directions for cerrosafe use.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  7. #7
    Boolit Grand Master

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    The throats on a revolver are on the front end of the cylinder(most are anyway, the 1895 Nagant is one exception)pin gauges are the easiest way to get a good measurement. You may find you have 6 different sized throats on a 6 shooter, not the best for accuracy but it can be fixed.
    Hell, I was there!

  8. #8
    Boolit Master
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    You are confusing terms. The rear of the revolver barrel is the forcing cone. You want to measure the chamber throats, the front portion of each chamber in the cylinder.

    These are examples of Starrett small hole gauges. I present this pair to illustrate the limited range of measurement. I am not the seller, and I only paid $5 each for mine. If you want to work on 38 Special, 44 Magnum, and 45 Colt revolvers, you would need these two. You also need a micrometer.

    An advantage of small hole gauges over pin gauges is that you can measure eccentricity. Rotate the gauge in the chamber throat and you can feel the tightest and loosest locations. Measure both. A pin gauge can only tell you the smaller measurement. A disadvantage of small hole gauges is they require more finesse to use. However, either one will get the job done satisfactorily.

    https://www.ebay.com/itm/L-S-Starret...ss!23061!US!-1

    https://www.ebay.com/itm/L-S-Starret...ss!23061!US!-1

  9. #9
    Boolit Grand Master



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    Quote Originally Posted by Tatume View Post
    You are confusing terms. The rear of the revolver barrel is the forcing cone. You want to measure the chamber throats, the front portion of each chamber in the cylinder.

    These are examples of Starrett small hole gauges. I present this pair to illustrate the limited range of measurement. I am not the seller, and I only paid $5 each for mine. If you want to work on 38 Special, 44 Magnum, and 45 Colt revolvers, you would need these two. You also need a micrometer.

    An advantage of small hole gauges over pin gauges is that you can measure eccentricity. Rotate the gauge in the chamber throat and you can feel the tightest and loosest locations. Measure both. A pin gauge can only tell you the smaller measurement. A disadvantage of small hole gauges is they require more finesse to use. However, either one will get the job done satisfactorily.

    Agree 100%. Pin gages are great but most people only have pin gages in .001" steps. I have mine in .0005 increments with specific sizes in .0001" but small hole gages are what I use the most of to check throats. I do recommend Starret. Some of the other brands I have been springy.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

    "Before you argue with someone, ask yourself, is that person even mentally mature enough to grasp the concept of different perspectives? Because if not, there’s absolutely no point."
    – Amber Veal

    "The Highest form of ignorance is when your reject something you don't know anything about".
    - Wayne Dyer

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Abbreviations used in Reloading

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
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check