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Plunk Test

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  • Plunk Test

    I'm new to reloading pistol ammo and had seen the plunk test mentioned numerous times.
    Is there an advantage to doing this vs.using a case length headspace gauge? I would think the gauge would be a more accurate way of checking. Prior to loading my first round, I purchased a Lyman gauge. Should I still perform a plunk test?

  • #2
    IMHO and experience, those case length gauges aren't worth wasting money on. I've been plunking my cartridges since I start loading decades ago and have yet to have problems.

    Honestly, because I've never used one, I'm not even clear on what they gauge.
    Is it the oal from case head to bullet tip?

    The distance from the case head to the ogive?

    From case head to the mouth?

    Or does it gauge the diameter of the resize brass, with or without the bullet seated.

    Either way, case length gauges do not represent your firearm chamber, only the chamber can determine the best oal for a pistol IMO.

    The way I load for an auto loading pistol is to seat them as long as possible while making sure they fit the magazine and feed reliably from it.



    • #3
      The plunk test is a far better case gauge than anyone's case gauges. Why, because the case gauge is a not an exact replica of the barrel in your pistol.
      The case gauge is made to work for all barrels which are not the same. All barrels are different.
      So why waste the money.
      "The United States Marine Corps is a drug and I am a recovering addict."

      "American by birthright… U.S. MARINE by the Grace of GOD!"

      "And on the 8th day God created Marines and like fish, we came from the sea!"


      • #4
        I thought it might mirror measuring a rifle chamber and loading accordingly, but much easier to accomplish.
        That was a few bucks I could have used toward the new P220


        • #5
          Live and learn; my orginal mentor always used a case gauge, but just starting out, I used his and never bought any. Fast forward a couple of years: I began reading this forum, and had dozens of mentors literally at my finger tips. Plunk test rules!


          • #6
            Good judgement comes from experience,
            and a lot of that comes from bad judgement.
            Mark Twain


            • #7
              Plunk Test Story.

              This fall I headed west for a elk bowhunt. Because I have a couple carry permits with a broad range of reciprocity, I loaded up my M60 .38 S&W. (Special Talo run).

              I grabbed a box of loads, . 38 Special Speer 158gr LSWC's, (I thought), and put 'em in my packer. When I got to camp, I pulled out my .38, and dropped a couple snake loads and 3 LSWC's in the cylinder. The cylinder wouldn't close. First time I ever loaded up a revolver that wouldn't chamber one of my handloads. So, a quick trip to town and I came back with a box of Federal LRN's.

              When I got back home, I pulled out that box of handloads, and tried them in my other .38's, same story. So I decided to check them with my caliper. Looked fine all round. Then I put on my reading glasses, and lo, .357 on the headstamp.

              Another lesson learned.
              Experience is what you get, when you don\'t get what you want ;-)


              • #8
                The plunk test is the best way. Variations in chambers, throats and rifling in different barrels makes it a must. I've had 45 ACP rounds that were fine in my 1911 come up a tad tight in my lone wolf barrel in the Glock. After adjusting the taper crimp a bit tighter it worked great in both.


                • #9
                  I believe the cartridge gauges are minimum SAAMI dimensions for a particular cartridge. I have a couple (somewhere) and they both caused me a few headaches. When I started reloading 45 ACP ('94) I tried one and had several headaches trying to get a round to fit the gauge (I couldn't use cast lead bullets, I had to really crimp, I even had to trim some of the brass). I took some of the failures and dropped them in the chamber of my barrel (s) and all went "plunk". I put the gauge away and plunk all my semi-auto pistol ammo (not every single cartridge, but about 10%-25%). I also have a gauge in 30-06 for my Garand. I tried way too many remedies to get the rounds to gauge and after a few weeks, new dies, and hours of "adjusting" I gave up and asked for info on a Garand forum. The first reply was "do they chamber?". Yep they chambered and fired fine (I later found a .010" distortion in the case rim from the ejected brass hitting the OP rod of my Garand causing the cases to not gauge)....

                  One thought came to me after discovering "plunking" I shoot cartridges in my gun, not in a gauge...
                  Last edited by mikld; 12-06-2018, 17:23.
                  I\'ve learned to stand on my own two knees...


                  • #10
                    If you use the plunk test, be sure to test them in the barrel you will be shooting them in. I've got five different 1911 in 45 ACP. One of my Frankenstein 1911s has a tighter chamber than everything else, what plunks fine in my Kimber, and works in my RIAs, American Tacticals, a Para, and the Kimber won't chamber in it. Chambers can vary.
                    "The fact that guns can kill another human being is the whole point. That\'s why they are so darn good at deterring violent criminals". Ann Coulter


                    • #11
                      The plunk test is primarily useful for gauging whether you have taper crimped the bell (applied during case expansion) out of your cases sufficiently. The plunk test will confirm that your ammunition will chamber in that barrel and that barrel only. It doesn't guarantee that it will chamber in your buddy's barrel if you needed to hand a magazine off to him in an emergency for example. If you use a factory Glock barrel for your plunk test and your buddy's glock has a "tighter" KKM match barrel, there's a real possibility that the round won't chamber properly if you crimped it just enough to plunk down into your barrel. Along the same lines, if you have multiple firearms that use the same caliber, you need to use the tightest barrel for the plunk test to guarantee that they'll fit all of your barrels.You adjust your taper crimp until the bullets plunks down into your tightest barrel and your final loaded rounds should be good to go in the rest of your firearms. You generally don't want to apply any more taper crimp than necessary especially in a high pressure pistol round. Just enough to pass the plunk and another .002"- .003" to give the round a little wiggle room. You don't want the cartridge taper crimped so much that the round is pushed forward past the barrel headspace index (is that what it's called? IDK).

                      Case gauges may be handier for gauging your final rounds COAL but the barrel is probably a better tool for establishing the appropriate amount of taper crimp unless you're loading bulk ammo intended to be used in firearms that you will never have any contact with-zombie apocalypse ammunition for example.

                      I haven't been reloading in a while and I'm getting ready to load up some 10mm. this was a good refresher discussion.


                      • #12
                        Originally posted by trouble View Post
                        You don't want the cartridge taper crimped so much that the round is pushed forward past the barrel headspace index (is that what it's called? IDK).
                        Impossible to do.

                        I used to give this possibility at least a little bit of credence,,, until I deliberately tried it last spring.

                        Shoved some 9mmP up in the dies so far they looked like .30 Mauser ammo, a solid 3/16 to 1/4 inch PAST the crimping ring, both my RCBS dies and a Lee Factory Crimp Die (NOT the post-resizing carbide version, just the straight-up crimp die).

                        In order to "de-headspace" the round,,, you'd have to swage the case down to bullet size.
                        The dies aren't that small, or you wouldn't get a bullet through them.

                        With soft (cast or plated) bullets you just make a bottlenecked round that still headspaces.
                        Use a jacketed bullet, you wrinkle the case, badly.

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                        My phone wouldn't focus that close (kinda like me any more), but it is properly headspaced, flush with the barrel extension, and you cannot shove it deeper, there is still far too much case mouth sticking out past the bullet to 'lose headspace'.

                        Try it sometime, you'll find out it's impossible.

                        Don't worry about screwing up cases (except with jacketed bullets), they'll iron right back out at full pressure, guaranteed.


                        • #13
                          I can't think of one good reason to apply a heavy taper crimp to a straight walled pistol case. I always remember this guy's story when I'm taper crimping high pressure pistol rounds for Glock pistols. I put a lot of thought and attention into setting up the taper crimp. I still prefer to do it in its own step in fact.

                          Bench Report: Anatomy Of My KaBoom!


                          • #14
                            That video is kinda weird: he says it was in a Glock, but the gun he displays is an M&P as is the one that has the failure.

                            At any rate, applying the taper crimp in a seperate final stroke of the press is often times a good way to go: I used to do that for .40 S&W as well as .45 acp. After several thousand rounds each, I felt comfortable enough to incorporate the process into the same 'pull' as bullet seating. I also believe that setting the expandind die to a minimum depth is key; I only expand the case enough to hold a bullet and with stand a gentle shake.


                            • #15
                              If you look at around 3:00, there's actual video of the blowout while he's shooting the Glock. It's pretty clear. His summary was that his cases were stretched and too long, the Glock factory chamber was over generous and unsupported, and the case was significantly over crimped. My RCBS expander dies bell the mouth such that the bullet "pops" into place when you hit the sweet spot and then it pops back out. I definitely keep the flaring as minimal as possible because I don't want to have to taper crimp any more than necessary.I load mostly 10mm and 460 Rowland for Glocks as far as semi-auto pistols go. 460 Rowland is pretty much operating at the maximum pressure that the Glock pistol is rated for. If you create a significant high pressure situation with a 460 Rowland or even a 10mm, something is more than likely going to break. So I try to be pretty careful. I like my guns and my fingers.