Pressure Signs: What, Where and Why?

[COLLECTOR 1]

Im betting the pictures of the wrecked firearms and peeled back barrels are a result more of a "blocked barrel".....

COLLECTOR 1

[Gwion]

looking at the primer for signs of pressure is actually the least accurate way of determining excessive pressure.

Measuring for case head expansion using a micrometer is how big boys do it.

So, what part of the case do you measure; just forward of the rim/head?

[happyhunter]

.

[on_one_wheel]

looking at the primer for signs of pressure is actually the least accurate way of determining excessive pressure.

Measuring for case head expansion using a micrometer is how big boys do it.

So, what part of the case do you measure; just forward of the rim/head?

The area immediately before the extractor grove.

Nick Harvey has a detailed writeup about this paticular method in his reloading manual.

I followed that method when I was in the quest for the hottest load my rifle could safely handle.

The end result was a load that goes so far beyond the typical reloading manuals max load that it's almost beyond belief.
Those super hot loads have improved accuracy because the increased velocity has reduced the affects of uncontrollable variables ... at the cost of barrel life of course.

[Gwion]

Cheers. I'll go back and re-read that section of th NH manual.

[BBJ]

The primers are cratered due to sloppy firing pin hole and on the pic below that you can clearly see a mark that looks like a bulge but after running through the FL die they are fine.

How does the firing pin hole translate back to cratered primers? Because the pin is too small and traps pressure?

[happyhunter]

The primers are cratered due to sloppy firing pin hole and on the pic below that you can clearly see a mark that looks like a bulge but after running through the FL die they are fine.

How does the firing pin hole translate back to cratered primers? Because the pin is too small and traps pressure?

The clearence between the firing pin hole and firing pin is excessive and allows primer cup metal to flow into the space.

[Gregg]

Measuring for case head expansion using a micrometer is how big boys do it.

Likely not many people with one lying around however.

[happyhunter]

looking at the primer for signs of pressure is actually the least accurate way of determining excessive pressure.

Measuring for case head expansion using a micrometer is how big boys do it.

Or anybody with the Hornady manual. You need one that does .0001". Big boys don't handload.

[Norton]

Big boys don't handload.

Huh?

[Gwion]

Big boys don't handload.

Huh?

Apparently big boys guns shoot best with factory ammo???

[Chronos]

Good article by Duane Siercks on what to look for with pics.
https://sierrabullets.wordpress.com/201 ... agnostics/

In both Cases #3 and #6, I would be suspicious of an Incipient Case Head Separation, even though the rings are higher up the walls of the cases, than I am personally used to. This applies if the cases were handed to me out of the blue and their rifles histories were unknown.
Whadayareckon?

I reckon the "smith" who chambered those rifles needs to go back to the loading dock where his skill set is probably more suited.

They look clearly like pick up on the reamer has marked the chamber and on firing the brass simply flows into the groove. I guess repeated f/l sizing and firing could work harden that area and eventually cause a failure but I think it might take dozens of firings at least

Chronos

[headspace]

One of my rifles, a 9.3x62 has flattened primers from every firing. The cases are Sellier & Bellott, and the primers were hard to seat right from the beginning. However the bolt lift is fine and the measurement at the web is fine too. I found out later that S&B brass seems to flatten primers pretty easily. SO yes, flattened primers are not an adequate indicator of excess pressure.