Plunk test

[wiiawiwb]

I've been using MBC 9mm, 147gr, bullet for years and check each round with both a case gauge and the pistol barrel. No problems. I just got a new batch of 147gr bullets from MBC and have reloaded 5 rounds. Each one pass the case gauge test but not the barrel test. I'm trying to figure out why that is happening.

The new rounds when dropped in the case gauge are perfectly level and drop out when I turn the gauge upside down. When dropped in the barrel, they plunk but will not twist nor will they drop when turned upside down.

Any thoughts about what is going on here?

 

[Rod47]

COL same? Maybe needs adjustment.

 

[LiveLife]

I am assuming the barrel/chamber is clean?

Paint the offending round with marker and see where the round is contacting the chamber.

 

[drband]

Have you checked your COAL lately. If it checks out longer than your standard, I would guess the ogive on the latest bullets is narrower, allowing them to seat slightly longer and possibly engage the lands.

color a loaded bullet with a sharpie and plunk it in the barrel. It should show marks if it touches the lands.

 

[fxvr5]

The magic marker method is explained here:

https://www.shootingtimes.com/editorial/reloading-tips-the-plunk-test/99389

 

[wiiawiwb]

The COAL is the same with old and new, which is 1.157. The round in red I decided to seat deeper and it has a COAL of 1.150. The barrel of the Glock is clean.

The only marks I can see are maybe on the case edge or rim itself.

 

[Telum Pisces]

The COAL is the same with old and new, which is 1.157. The round in red I decided to seat deeper and it has a COAL of 1.150. The barrel of the Glock is clean.

The only marks I can see are maybe on the case edge or rim itself.

I can see a difference with my eyes unless it's an optical illusion. Red brass looks longer than the black ones. Check brass length

 

[LiveLife]

How about case wall thickness?

Are they both same headstamp brass?

 

[wiiawiwb]

They are all Starline brass. The red does look longer in the picture but measures out the same.

 

[fxvr5]

Stick them back in the chamber and keep rotating them or moving them up/down until you can see where the MM is rubbed off and where they are sticking.

 

[wiiawiwb]

The black MM wasn't showing anything so I removed all MM and started again using just red. On both, the marks look to be along the bottom.

 

[fxvr5]

OK. Measure that location. And if you put them back in the chamber you should notice that the rear of the cartridge won't wiggle back and forth at all like a new factory load.

 

[wiiawiwb]

...

 

[fxvr5]

What is case diameter at that point?

 

[wiiawiwb]

It is .386 which, oddly enough, is the same diameter with several of the rounds I have, from the old MBC bullet, and they plunk, spin, and fall out without problem.

Another piece of information. The barrel I'm using is a brand-new Glock 43-X, 9mm with less than 50 rounds through it. The previously-reloaded ammo passed the plunk test without issue, its the new ones that are the issue.

When I try the new reloads, using the new BC bullet heads, they do pass the plunk test with my Glock 17 which is also 9mm.

 

[jonb32248]

One on right has a wear line a third the way up from rim.

 

[LiveLife]

If you do not have the same problem with factory ammunition, it's likely your reloading process.

However, it's odd that the finished rounds are sticking in the barrel's chamber, which often is larger in dimensions than the cage gage. Often members report the rounds are passing the barrel but sticking in the case gage.

Are you sure the bottom of bullet nose is not rubbing the start of rifling? You are able to freely spin the chambered round in the barrel?

If you can't freely spin the chambered round, try seating the bullet deeper like .005" and see if the round drops freely from the barrel.

 

[fxvr5]

Let's speed things up. Push the bullet deeper, say 1.120 OAL. See if that fits. If not, recrimp and try again.

I've heard some of the new Glock barrels have a short throat.

 

[murf]

a case gauge checks the fit of the case, not the loaded round. if your barrel has a short, or no lead, the loaded round will fail the plunk test because the bullet is touching the barrel lands (as stated a few times above). seat deeper and redo the plunk test (as stated a few times above).

luck,

murf

 

[Toprudder]

The case gauge in no way simulates the chamber forward of the case mouth. Test it by dropping a bare bullet through the gauge, it will most likely fall through. The case gauge is supposed to be minimum SAAMI spec, so it should be smaller than the chamber in the barrel - up to the case mouth. So, the problem is most likely forward of the case mouth. Either the bullet is seated too long and contacting the rifling, or the seating process has scraped some lead/coating off the bullet. I suspect the profile of the bullet might have changed slightly and needs to be seated deeper.

 

[mcb]

There is a difference between a case gauge and a chamber checker. A case gauge checks case length and shoulder location if it's a bottle neck case. And is likely not made to minimum diameters.

A chamber checker, if made right, is cut with min spec. chamber reamer and includes minimum free bore and throat. It should be tighter than the chamber in your gun so you know if it passes the chamber checker it will easily chamber in your gun. My 450 BM chamber checker even has rifling. Most of my pistol chamber checker are bored to give diameter with no rifling.

 

[ArchAngelCD]

Seat true bullet deeper into the case and be sure to start the bullet correctly so there is no bulge at the bottom of the bullet.

 

[wiiawiwb]

Thanks everyone, I really appreciate it. I will seat a few rounds deeper and let you know how they turn out. Thanks again.

 

[Toprudder]

There is a difference between a case gauge and a chamber checker. A case gauge checks case length and shoulder location if it's a bottle neck case. And is likely not made to minimum diameters.

You are very correct about bottleneck rifle case gauges, thanks for mentioning that. This discussion is about 9mm, though, and case gauges for those are cut to SAAMI min spec. At least the ones that I have are.

 

[PWC]

I don't know, maybe it's just me, but if I'm reloading, I have the manuals, and cartridge specs available, and if I have a problem like this, first thing I do is grab a magic marker, then the calipers and a known good cartridege or barring that, the SAAMI specs. The problem becomes visible, and fix becomes obvious.