Plunk Test clarification

B

Billglass

New member
I’m hoping to get some clarifications for the proper uses and interpretations of the plunk test for reloading semi-auto pistols.

PLUNK TEST FOR CASE ONLY MEASUREMENTS
First, my understanding, for my specific barrel, I can sort through resized semi-auto cases and find a case that the case mouth is resting on the ledge in the barrel and the bottom of the case rim is level with the top of the barrel hood. This is depicted as the 2nd case from the left
in Unclenick’s image.
If I measure this case length with my calipers, I will get the “headspace” of my barrel.
This case length is ideal for my gun. Starting with cases only of this length, I would seat bullets deep enough that, when plunked do not have the case rim coming above the barrel hood.

Secondly, if I plunk test a resized case and the case rim is above the barrel hood, the case needs to be trimmed to my measured “headspace”. (OR if I measure the case with my caliper and it exceeds my “headspace” the case needs to be trimmed. This the 4th case from the left in unclenick’s image. I’ve read that since semi-auto cases rarely grow, and actually shorten – so this is an unlikely condition.

Thirdly, if I plunk test a resized case and the case mouth is resting on the barrel rim, but the case rim is below the barrel hood, the loaded ammo using these short cases will headspace on the extractor and a tilt could be introduced – with some accuracy loss. Again, the cases can be measured with a caliper and compared to my gun’s headspace.
Does this condition cause damage or extra wear on the extractor? Or the gun?

PLUNK TEST FOR ASSEMBLING LOADED AMMO

From what I read on many forums, the plunk test is mostly used to determine the COL of a certain bullet/gun combination and a “PASS” is that the loaded ammo drops into and comes out of barrel without interference. Case length is not measured or considered.
Since most cases are short, I assume most load their ammo that will end up head-spacing on the extractor or if they notice the case rim is below the barrel hood, will seat the bullet longer until it is level not realizing they are now head-spacing on the bullet.

I would appreciate any and all feedback
 
I don't think you get much of a plunk sound from an unloaded case, but you can certainly gauge it by insertion to the chamber.

If you look closely at my drawing, you will see it is actually the third from left that has the outside face of the head level with the hood, though in that case because it is held there by the bullet. The number 2 is closer to what is normally seen, which is headspace a little longer than the case. Regardless, level with the hood is a correct for measuring headspace as long as, when in battery, your hood is firmly against the breech face in the slide. If it gets thrown forward of that position, either during chambering or during firing, then your actual headspace is longer. If your barrel hood was fitted to your slide, then you have no problem with it.

For gauging the brass, I would resize the brass first, as its length grows during resizing because the brass has to flow somewhere when you squeeze it narrower. The length of the case before resizing is of academic interest, but it's not what your reloads will have. Seating a bullet will shorten the case very slightly by reversing the sizing die's squeeze for a the length of the seating depth, so when you drop the loaded round it (makes the plunk sound), check the position of the head with respect to the hood again, just to make sure it wasn't enough change to matter. It normally is not.

If a case came out above the hood, then, yes, it would need trimming. I can say that in forty years and probably at least a couple hundred thousand rounds of .45 Auto, I've never seen a .45 Auto case that required trimming. That's because they get shorter with each load cycle, opposite to what a rifle case does, though the shortening is small; on the order of half a thousandth per cycle.

You are correct about the loaded ammo plunk test. I'll only add that when you are headspacing on a lead bullet, it cushions the landing so there isn't much of a plunk noise. That noise comes from the rim hitting the chamber shoulder smartly.

The image Bill is referring to:
attachment.php
 
Great image!
Someone really put effort into that.

I disagree with #4, mostly nit picking, but the image shows a cartridge that will keep the barrel/slide from locking at full battery, not a failure to feed.

The first image shows a case too short, or crimped WAY too much,
While it *Shouldn't* hurt the extractor, it's certainly NOT recommended.
The extractor claw will simply try to pull the cartridge back against the bolt face.

Extractor claw won't lock on the rim of the case until the slide is fully forward, so it shouldn't create an unsafe condition, but if the round is too far in the chamber the case might not extract correctly.
In blow back firearms, the case is coming out 99.99% of the time, but without the claw in the extraction groove, the case will often times not eject properly,
'Stove Pipe' failure to eject is common when the extractor doesn't hold the case against the bolt face all the way back to the ejector.

I had a 1911 clone in here not too long ago with that same issue, the guy was swearing it was the pistol, but I couldn't make it malfunction, when he brought his ammo (import crap) the rim was too thick, groove too narrow, and the claw simply couldn't lock onto it consistently.

Guys that get carried away with crimping have this issue fairly frequently and cuss the pistol.
The bell/taper on the case mouth is only supposed to be straightened, not bent in on the bullet.
That case mouth is supposed to sit on a lip in the chamber to determine headspace,
Too much crimp let's the case mouth miss the ledge/lip and drop too far into the chamber...

And just for the record, I've NEVER relied on a 'Plunk' test for sizing test, and I used to run a speed gun.
There is a whole lot of things a 'Plunk' test won't tell you,
Nothing beats a proper case gauge for 'Last Word' check of case sizing or loaded rounds.
 
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Even an empty case 9MM trim .744 headspaces longer than the hood with my CZ-75B.

Works fine with commercial and my reloads that are less than .754, crimped to .379.

I guess the hood must allow for it.
 
For clarification on the plunk test for loaded rounds the round should spin freely after it is dropped in. If not, then the bullet COL is too long and it is catching on the lands.
 
Even an empty case 9MM trim .744 headspaces longer than the hood with my CZ-75B.
Click to expand...

It's the same with my Beretta 92fs. The remaining part of the hood resides on the slide's breech face, so to speak.

When I plunk test for my Beretta, I start with a empty case that has been through my Lee FCD - doesn't work with a conventional crimp die. The empty case has a very positive "plunk" when its mouth hits the chamber shoulder; and that's my reference.

Turns out that most every bullet will plunk too long for the mag anyway; so it's kinda moot. I've gotten to just using the bullet's OAL dimension in their manual.
 
Turns out that most every bullet will plunk too long for the mag anyway
Click to expand...

The "plunk" test for loaded rounds is to tell you if the round fits the chamber. It won't, and can't tell you if the round will feed from the magazine.

Depending on the nose profile of the bullet, and your magazine's actual clearance you could have rounds that won't feed from the mag, at all, or rounds that will only feed the top 3 or 4 rounds from the mag, and they could all pass the plunk test and chamber.
 
That's a good point
I've made several dummy rounds to find the max COL for my mags for each semi-auto i have when I first got the gun. It's one "working" max length that goes into finding all the boundary lengths. But I've only had to determine it once, regardless of bullets used thereafter.
 
The "plunk" test for loaded rounds is to tell you if the round fits the chamber. It won't, and can't tell you if the round will feed from the magazine.
Click to expand...

Right. I know. Poor choice of words on my part.

I just meant to say if I set the OAL so long to where the bullet is touching the lands, it will likely be too long to fit in the mag. " . . . plunk too long for the mag" was horrible wording.
 
"I've gotten to just using the bullet's OAL dimension in their manual."

Where the plunk test is invaluable is with bullets that the manufacturer doesn't provide the COL .....like x-treme and other plated bullets:confused:
 
Jeephammer said:
I disagree with #4, mostly nit picking, but the image shows a cartridge that will keep the barrel/slide from locking at full battery, not a failure to feed.
Click to expand...

It can do both. Often, when the cases are protruding, unless the bullet is a short rounded edge nose design you start to get magazine lift failures or jams against the feed ramp. Also depends on whether the gun has been tuned for feed reliability and how good your mags are. In any case, it's generally not helpful to have your cartridges loaded that way, though I have gotten away with a little protrusion with lead soft enough that the slide can force it into the throat that much. Still don't recommend it.
 
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