Cartridge Overall Length

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    J

    JB01

    Member
    Nov 11, 2017
    99
    Plunk Test Question

    Please pardon my ignorance. I am assuming that a "plunk test" is placing a cartridge into a barrel chamber without using force to determine if the cartridge will freely enter the chamber and seat to the correct depth.
    If my assumption is true and one uses a cartridge which headspaces on the case mouth, then the over all length (OAL) of such a cartridge may grossly exceed the recommended OAL and not fail the "plunk test" until the bullet hits the lands. Is this true? Thank you.
    JB
     
    J

    JB01

    Member
    Nov 11, 2017
    99
    Please pardon my double submission. When I submitted the first reply, I received an error message indicating I could not complete the submission because the message was too short.
    JB
     
    outrider58

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    50,026
    JB01 said:
    Please pardon my ignorance. I am assuming that a "plunk test" is placing a cartridge into a barrel chamber without using force to determine if the cartridge will freely enter the chamber and seat to the correct depth.
    If my assumption is true and one uses a cartridge which headspaces on the case mouth, then the over all length (OAL) of such a cartridge may grossly exceed the recommended OAL and not fail the "plunk test" until the bullet hits the lands. Is this true? Thank you.
    JB
    Click to expand...

    You win the "Obvious observation" award. It will probably fall on deaf ears however. :clap:
     
    M

    Mark K

    Active Member
    Sep 29, 2013
    280
    Colorado Springs, CO
    JB01 said:
    If my assumption is true and one uses a cartridge which headspaces on the case mouth, then the over all length (OAL) of such a cartridge may grossly exceed the recommended OAL and not fail the "plunk test" until the bullet hits the lands.
    Click to expand...

    That's what I was thinking too, when I wrote this in Post #5:

    Mark K said:
    Re: plunk test. Yeah, that would detect whether a cartridge is (way) too long, but not if it's too short...?
    Click to expand...

    That's why I think the plunk test would be of limited value to test whether the bullet is seated too far or not far enough. It's probably more useful to check taper, or overall dimensions of the casing...
     
    L

    lazarus

    Ultimate Member
    Jun 23, 2015
    13,730
    Mark K said:
    That's what I was thinking too, when I wrote this in Post #5:



    That's why I think the plunk test would be of limited value to test whether the bullet is seated too far or not far enough. It's probably more useful to check taper, or overall dimensions of the casing...
    Click to expand...

    It’s not. A lot of barrels have short throats. That’s part of the SAMMI spec that is often violated IMHO.

    The ogive of the bullet is going to heavily influence this.

    Example, my Sweson Glock 17 barrel has a very short throat. With RMR 115gr FMJ I can seat to 1.092”. Any longer and if rams the rifling. Missouri LRN 115gr coated I can load to 1.098” COAL before it touches the rifling.

    My German P1 passes a plunk test at 1.120” even. Just fine, both bullets.

    In 32acp my Vz70 has to go .01” under listed COAL for Berry’s or the same (have to load at SAMMI min) bullets ram the rifling. My Cz50 has no issues even loaded slightly longer than SAMMI COAL max.

    If you haven’t crimped properly/removed the case flare it also might not plunk in to the chamber properly.

    Same reason people use case gauges. Just more accurate to use the barrel of the gun you are going to shoot the round in.

    A plunk test isn’t for checking the actual COAL. That’s what your cartridge gauge and/or calipers are for. It’s to check gross errors in crimp, case length and max COAL/short throat of your gun. Sucks to find out what worked great in your other 5 guns jams the action shut in your 6th gun.
     
    Pinecone

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    JB01 said:
    If my assumption is true and one uses a cartridge which headspaces on the case mouth, then the over all length (OAL) of such a cartridge may grossly exceed the recommended OAL and not fail the "plunk test" until the bullet hits the lands. Is this true? Thank you.
    JB
    Click to expand...

    Yes, but the other part of the test is to see if the rounds fit into the magazine.

    Many times, the magazine is the limiting factor to max COAL.
     
    M

    Mark K

    Active Member
    Sep 29, 2013
    280
    Colorado Springs, CO
    Thanks. I knew plunk tests were good, but I didn't know how good...

    Nobody ever answered... Is it a problem if I'm getting some muzzle flash with the G42, at the max load? Does that mean there's excess powder going out the bore after the bullet launches? I.e., too much charge?
     
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