The Plunk Test explained

[oremike]

I found this you-tube video and thought it explained it well:

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[Certaindeaf]

Didn't click but it's a sound thing.

 

[DizzyJ]

Great explanation. I found out years ago just because the 9mm cartridge will chamber in the Beretta does NOT mean it will chamber in the Walther for the very reason he mentions both with ogive profile and chamber depth variation.

I make it a point to hand cycle 10 consecutive rounds through the gun before proceeding to crank out a couple thousand.

 

[oremike]

That's why I call all my guns "test fixtures" for my ammo business*. It's got to fit or it don't ship.
*Also being test fixtures makes them a tax write off.

 

[Caveman Jim]

I remember having a problem with 9 mm Montana Gold 124g HPs, I was told to load them with XTP data at 1.15", when it didn't plunk I narrowed it down to 1.09".

 

[ARFrog]

I case gauge and plunk test my 9mm reloads. Never heard about the push and twist in addition to plunking. Will give it a try. Thanks.

 

[Mikej]

I remember having a problem with 9 mm Montana Gold 124g HPs, I was told to load them with XTP data at 1.15", when it didn't plunk I narrowed it down to 1.09".

Montana Gold 115gr are the same. A longer bearing surface than what was used in the loading books. I have to shorten down to 1.095" for the regular old factory guns. And 1.085" for a Kimber Pro Aegis, and 1.070" for the fancy Tanfoglio.

 

[Koda]

I get what hes doing but why wouldnt a round set to saami specs fit any chamber? Wouldnt that indicate somethings wrong with that chamber?

 

[ma96782]

The EASY version.....



But, I admit that some adjust may be necessary from time to time.


Aloha, Mark

 

[oremike]

I get what hes doing but why wouldnt a round set to saami specs fit any chamber? Wouldnt that indicate somethings wrong with that chamber?

No, not all bullets are the same look for example at a 30 caliber Hornady 150gr SP and a Hornady 150gr RN. Both the same manufacturer and weight but completely different profile. The key measurement is from the case mouth to the olgive that's the free bore or distance to the rifling. In the Hornady book for 30.06 those two bullets show a COAL of 3.210 for the SP and 3.000 for the RN. that's all most a quarter of an inch difference. The Maximum COAL is still another measurement at 3.340 Looks like they are using E-LDX match bullets to get that number, but I'd bet they are single loading not feeding from a magazine at that length.

 

[Koda]

No, not all bullets are the same look for example at a 30 caliber Hornady 150gr SP and a Hornady 150gr RN. Both the same manufacturer and weight but completely different profile. The key measurement is from the case mouth to the olgive that's the free bore or distance to the rifling. In the Hornady book for 30.06 those two bullets show a COAL of 3.210 for the SP and 3.000 for the RN. that's all most a quarter of an inch difference. The Maximum COAL is still another measurement at 3.340 Looks like they are using E-LDX match bullets to get that number, but I'd bet they are single loading not feeding from a magazine at that length.

Saami doesnt measure to the ogive. I realize ogive geometry is uncontrolled and varies, and i understand that there are times and reasons when its ok to deviate from saami specs (eg, coal) but its also my understanding that if you stay inside saami dimensions its supposed to assure fit in all saami chambers?

 

[Mikej]

Saami doesnt measure to the ogive. I realize ogive geometry is uncontrolled and varies, and i understand that there are times and reasons when its ok to deviate from saami specs (eg, coal) but its also my understanding that if you stay inside saami dimensions its supposed to assure fit in all saami chambers?

Saami specs don't determine the ammo. Saami determines the chambers specs. Loading books tell what recipes they tried and the resulting pressures and velocities.

 

[Koda]

Saami specs don't determine the ammo. Saami determines the chambers specs. Loading books tell what recipes they tried and the resulting pressures and velocities.

The way i understand it is saami determines the ammos dimensions and the chambers dimensions and pressures.

Loading books try to stay inside those dimensions and pressures...

 

[WillametteWill]

I learned some stuff, thanks for posting. I do hate that YouTube algorithms like 8 or better 10 minute videos when a much shorter time will do.

One thing not addressed, especially with the high pressures of 9mm, is that deeper seating can spike the pressures rapidly. I had a bullet that had to be set ridiculously deep to plunk compared to the recommended COAL from the manufacturer. There is zero chance I will ever use the bullets. With the truncated cone, they hit the rifling much sooner than traditional round nose and other TC bullets I have used.

Appreciate the info OP!

 

[Mikej]

Loading books try to stay inside those dimensions and pressures...

Loading books give you the results of their recipes/loads. That's all. Saami gives working/safe/Maximum pressures, and the loading book's print recipes that stay within those pressures.

 

[Mikej]

recommended COAL from the manufacturer.

That COAL isn't what is recommended, it is what they deemed suitable/appropriate and safe for us to use. At least that's the way I look at it. When I run my COL shorter than the book has I load well below max. I also consider a slower powder to be less susceptible to pressure spikes. Hence my use of HS-6 in 9mm and .40.