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Pistol Chamber measure method

Discussion in 'Handloading and Reloading' started by gifbohane, Jan 23, 2020.

  1. gifbohane

    gifbohane Member

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    I am still trying to get my new CZ75B squared away. I have the usual smaller chamber problem and trying to get to proper OAL with a leade of .015. One of the guys recommended that I take one of my fired 9mm cases, flare it and lightly place a bullet in it and press it lightly into the chamber to determine my chamber length. Presume that I resize it before "belling" it.

    Now if I do not size it before belling the bullet slides deep into the cartridge. If I do resize it and THEN bell it, then the bullet will not go deep into the chamber for proper seating. It sits high on the barrel. If I press very hard then the bullet will get stuck in the chamber as I remove the cartridge and I must push the bullet out of the barrel with a small cleaning rod. I have to be missing something here. Can anyone help or point me to a video?

    If not I am going to buy a Sinclair chamber measure...I want to get this right.

    Also extreme accuracy is not important with this firearm.
     
  2. FROGO207

    FROGO207 Member

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    What I do is make a dummy round without a primer and intentionally make it long. The max that will fit the mag. Then with the barrel removed try the plunk test. Then screw the seating stem in 1/4 turn and try again. Repeat until the round drops in with a plunk to the correct length and falls out when tipped. That is my depth if three rounds made that length feed without problems after you put the gun back together. If you want after a load workup try changing the depth a bit either way as you check for improvments on target.
     
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  3. Texas10mm

    Texas10mm Member

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    Shine a light into the barrel. If the rifling starts right at the end of the chamber then you have a 9mm barrel that's not cut to SAMMI spec, but don't worry, almost no 9mm barrels are cut correctly.

    IF the barrel isn't hardened then it's pretty simple to have it throated with a correct leade.

    Cylinderhone on Facebook, or DougGuy over at castboolits (it's the same guy) can cut a correct throat in the barrel for you.
     
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  4. higgite

    higgite Member

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    I do similar to Frog, start long and crank the seating stem in 1/4 turn at a time until the dummy round falls free of the chamber due to gravity alone. Then I pull the bullet, turn the seating stem back out 1/4 turn and start the plunk sequence again but just turn the seating stem in a small amount each time until the round falls free due to gravity again. That’s my max COL for that bullet in that pistol. Then you can measure and set the seating stem to give you .015” or however much bullet jump you want.
     
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  5. Innovative

    Innovative Member

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    gifbohane . . . .

    There are a lot of handloaders experiencing that exact symptom, especially with the 9mm and 40 S&W. Most of the time, it is a case width problem - not a headspace problem. You should always use a drop gauge to make sure ALL of your completed handloads will fit inside by gravity alone. I wrote a good article on this subject here: http://www.larrywillis.com/Glock.html It explains why Glocks have more problems with this than most other handguns.
     
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  6. ATLDave

    ATLDave Member

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    Trial and error is the usual way to deal with this with CZ's and other short-throated barrels. Make a round with no powder or primer. Seat the bullet, test, and then adjust seating stem and seat deeper until you get there. No need to make it difficult.
     
  7. ATLDave

    ATLDave Member

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    In CZ's, it is typically an ogive/rifling interference problem. They have short throats. Many rounds that will chamber in something like a Glock won't fit in a CZ.
     
  8. LiveLife

    LiveLife Member

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    +1 and I also spin the fully chambered dummy round to ensure the ogive (especially the bearing surface) of the bullet is not hitting the rifling.

    You know, bullet nose profile is sometimes not that consistent and bullets can be seated crooked. ;)
     
  9. jmorris

    jmorris Member

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    Does the hood contact the breechface when locked up?

    If so take your rounds and plunk them in the barrel and you can use a square to see how much gap there is.

    Kind of like this but with a square and feeler gauges you can get an accurate number.

    22D235E6-9D04-426E-9A97-24B48B5235A9.jpeg

    2C80E5E4-31FA-4307-BDA4-2FA8AC167871.jpeg

    It would not surprise me at all if you learned that some 9mm bullets (profile dependent) .015” off the lands are now too long to fit in the magazine, though.
     
  10. mrawesome22-250

    mrawesome22-250 Member

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    Size a case then flare it. Cut a vertical slit down the center of the case to weaken it. Now barely seat a bullet. Slide this into the chamber and push the case in as far as it will go. Take a cleaning rod and insert into muzzle and push the cartridge out. This is max oal for this particular bullet.
     
  11. higgite

    higgite Member

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    If you cut slits in the case, you don’t need to flare it. You can easily slide a pullet partially in and then slide it into the chamber. A flare can cause the case to drag when you push on the bullet with a rod through the muzzle, driving the bullet farther into the case and giving you a false max COL. Be sure to deburr the external edges of the slits for the same reason. And make sure the empty case plunks by itself before inserting a bullet.
     
  12. BiknSwans

    BiknSwans Member

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    My favorite method to determine the maximum OAL is described in a thread
    Determining Max OAL
    By Laughingdog, June 7, 2014 in General Reloading
    https://forums.brianenos.com/topic/196723-determining-max-oal/
    I think it's easier, especially if you are using a new bullet and want to know the maximum OAL for multiple firearms.
     
  13. mdi

    mdi Member

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  14. higgite

    higgite Member

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    From the brianenos link:
    How do you assure that the bullet is sitting straight in alignment with the chamber and not cocked to one side without a case to hold it straight?
    I’m sure that method works for you, but FWIW, I tried it with 3 different bullets in a Sig P226 barrel and got some relatively wide variations.
    PD 124gr JHP (.420-.433”)
    Xtreme 124 plated HP (.461-.475”)
    Zero 115gr JHP conical (.469-.476”)
     
  15. Lennyjoe

    Lennyjoe Member

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    I also use a black permanent marker and color the bullet before seating to see if it moves out upon removal. More so for bolt action rifles when forced into the lans but is nice to check and see for pistol as well.
     
  16. BiknSwans

    BiknSwans Member

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    Interesting. I didn't have any problems - the bullet self-aligns when it hits the lands. I place the barrel vertically on the bench and drop in the bullet.

    I have measured maximum OAL only with coated bullets, Acme 124 RN (new and old profiles), Acme 147 FP, Precision 147 TC, Acme 180 FP (new and old profiles) and Bayou 180 TCG. The barrels I used were M&P 9mm, M&P .40 S&W, Storm Lake .40 S&W to 9mm conversation barrel, and Beretta 9mm. The case gages I used were a 9mm Midway gage and an L.E. Wilson .40 gage. The Beretta allowed the longest OAL and the L.E. Wilson gage the shortest, actually too short.

    The next time I'll double check the alignment and take even more measurements as a double check. Thanks.
     
  17. roval

    roval Member

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    check this out from my video on my cz97b. i just seat the bullet shorter till it plunks in and pops out and how a longer bullet doesnt fall out.

     
  18. BiknSwans

    BiknSwans Member

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    I ran through the OAL procedure again yesterday, and this time had some issues. I was using Acme 147 grain flat points. When I dropped the bullet in the barrel and tried to measure the distance from the reference surface to the bullet, I kept getting different numbers. It turned out the because of the slope of the ogive, it was easy too push the bullet in farther into the lands. Any force at all using the calipers increased the measured distance. Round nose bullets with their blunt profile must just touch the lands and stop, making the measurement easy and consistent.

    The classic plunk test would seem to be the best way to determine the maximum overall length when using some flat point bullets. The case mouth sitting on the ledge in the barrel would provide a stable condition for plunk testing.
     
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