Plunk Test - OAL and Leading ?s


November 20, 2013, 02:02 PM
I'm new to the forum and posted these questions in another thread where it did not belong. Subsequently I read the thread about the plunk test which I'd heard of but never seen explained so well.

I have reloaded about 1200 45 ACP - and 200-300 9mm and never used the plunk test, rather used an OAL (after testing some slightly longer and working my way down to OAL cited by others in a 1911 forum - memory serves 1.255. Diameter with taper crimp was set to same as factory FMJ and have had no lead shaving. I have not tested for pushback either.

Am I lucky to not have problems? Do I read the plunk test correctly to measure for an OAL and diameter that are flush or a hair below to maximize accuracy? My current OAL has fed and ejected from two different 1911's with no issues.

I also don't really know how to recognize leading. I've been told little balls around the rifling. My Dan Wesson barrel has had most of the 1000 rnds of LSWC shot through it and after cleaning there are a few gatherings of material - but not necessarily in the rifling (I'm fudging description because these old eyes needed more light and a magnifying glass - which I haven't used yet). I will tonight at home.

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November 20, 2013, 02:55 PM
The plunk test is to confirm that the bullet is not getting into the rifling. Most leads on 45's do not cause a problem unless you had a barrel custom fitted and the gunsmith set it up on tighter tolerance. Since your have multiple 45's you may want to determine which barrel is tighter. Then use it as your reference barrel for sizing.

Most 45 Lead projectiles are 0.001" larger than the jacketed counter parts. This sizing is to ensure the lead seals off and prevent leading. You will know what leading looks like once it happens. Since your not having a problem don't sweat it.

November 21, 2013, 12:27 PM

This is probably the single best information on leading. If you have it bad enough to cause a problem you will know it. If you cannot see any issues looking in your bore you're fine.

Are you shooting commercial cast, or your own cast? Bullet fit is crucial, also ensuring the bullets are age hardened to the proper BHN is crucial if you are casting them yourself.

November 21, 2013, 02:19 PM
I'm shooting 200gr LSWC bullets mostly from MO bullets and did buy 500 from Alpha Bravo.

Is the "plunk test" the same as a "slug test"? I have a serious need to examine all my barrels and my rounds with the plunk test.

November 21, 2013, 10:50 PM

Here's a nice thread on the plunk test -

November 22, 2013, 11:08 AM
Thanks. Yes, I've read that thread and will be checking all my measurements this weekend with dummy rounds I've created at varying OAL's.

I also haven't tried the chambering test someone recommended to check on the best OAL for feeding - load the round slowly by holding onto the slide and letting it advance a little at a time to see if/where there's any hangup.

What is a slug test???

November 22, 2013, 12:50 PM
Slugging is to determine the size of your barrel or throat. So you can get proper fit bullets when loading lead. Normally 0.001" over the barrel or throat size.

November 22, 2013, 01:19 PM
To determine the working OAL/COL, start with the max OAL/COL from the barrel drop test and load the round in the magazine.

Then either lock the slide back or pull back and release without riding the slide to better duplicate the slide cycling forces.

If the max OAL/COL reliably feed/chamber from the magazine then it's the same as the working OAL/COL. If it doesn't, incrementally decrease the OAL/COL until the round reliably feed/chamber from the magazine. This is your working OAL/COL.

November 22, 2013, 01:36 PM
Thanks, I have a bit of checking to do.

November 22, 2013, 01:48 PM
Make sure you crimp/debell before plunking!

I had some 9mm loads get very scarily short before realizing the bell was stopping the case from proceeding.

November 22, 2013, 02:39 PM
Yes, I have varying lengths of dummy rounds made already - though they all have the same diameter, which is what I've been shooting and is the same as factory rounds.

I do find the 45 ACP so much easier to work with than the 9mm, my bell on the 9mm is quite small already.

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