Measuring pressure ring and case head.

[Mtstalker]

I ran across a video on measuring pressure ring and head exspansion on cases for finding max loads. Unfortunately he didnt explain where to measure or how. I did a bunch of searchs on here and couldnt find a solid answer on where to measure the pressure ring or case head exspansion and what is max exspansion. Some say .0002 others say .001! Thats a big jump. Some say measure extractor groove others say on the body at the edge of the groove? Now i see some guys use case head exspansion and pressure ring exspansion interchangeably, i always thought the pressure ring is the area after the web where brass grows to fit your chamber. I have one rifle that has a large chamber ( you guys helped me with that one) and leaves a distinct one side bulge on the case. The cases had to grow .011" to fit the chamber, in the article i found it said from new to fired only .001" growth is acceptable for pressure ring growth. I didnt think that was accurate due to chamber and brass size difference. Example if you have sammi min sized brass and a sammi max chamber. So where should i measure and how much growth is acceptable? And where is the pressure ring exactly? I hit the point that im done chasing excessive speed and want good accuracy and great brass life. And the whole reason im asking is because in 4 reloading manuals i have there max loads listed that are the starting load in a diffrent book. Just trying to stay safe. Thanks guys.

 

[fguffey]

I ran across a video on measuring pressure ring and head exspansion on cases for finding max loads.

Based on your research it appears they are just making it up as they go. Before social media it had nothing to do with 'maximum pressure', back then a few reloaders understood factories tested and developed their loads so they purchased and fired factory ammo for a standard. They measured the diameter of the case head before firing and again after firing. It was decided in the old days a normal case head expansion for factory loaded ammo was .00025". A reloader when developing loads tried to duplicate the .00025" expansion for the first firing. If the case head expanded .0005" they were above factory pressures.

F. Guffey

 

[Mtstalker]

But where are they measuring? Thats what i cannot find a answer on.

 

[LHSmith]

I ran across a video on measuring pressure ring and head exspansion on cases for finding max loads. Unfortunately he didnt explain where to measure or how. I did a bunch of searchs on here and couldnt find a solid answer on where to measure the pressure ring or case head exspansion and what is max exspansion. Some say .0002 others say .001! Thats a big jump. Some say measure extractor groove others say on the body at the edge of the groove? Now i see some guys use case head exspansion and pressure ring exspansion interchangeably, i always thought the pressure ring is the area after the web where brass grows to fit your chamber. I have one rifle that has a large chamber ( you guys helped me with that one) and leaves a distinct one side bulge on the case. The cases had to grow .011" to fit the chamber, in the article i found it said from new to fired only .001" growth is acceptable for pressure ring growth. I didnt think that was accurate due to chamber and brass size difference. Example if you have sammi min sized brass and a sammi max chamber. So where should i measure and how much growth is acceptable? And where is the pressure ring exactly? I hit the point that im done chasing excessive speed and want good accuracy and great brass life. And the whole reason im asking is because in 4 reloading manuals i have there max loads listed that are the starting load in a diffrent book. Just trying to stay safe. Thanks guys.

From Mike Ratigan's book "Extreme Rifle Accuracy": "After the brass is up to full size, reducing the length and body diameter by about 0.0005" is all that is required." A diagram accompanying this procedure shows notations on a cartridge at the body/shoulder junction and also immediately above the extraction groove on the body stating "reduce dia. 0.0005". The "pressure ring" relates to bullets....this is from the above referenced book's glossary "a small oversize ring on the heel of some bullets, produced during their manufacture." (Usually found on flat base custom bullets).
This process describes optimum sizing as a result when the proper fl die is used AFTER cases have been completely fireformed to your chamber.

 

[LHSmith]

On a fully FF 6 ppc case, we can determine proper sizing by using a calipers and taking a reading at the shoulder/ body junction- lock this measurement, then after sizing the calipers should drop approx. .0100 down the case. Note the PPC case has about 0.010" taper per inch.

 

[jpretle]

OP, Bob Hagel in his book, "Guns Loads and Hunting tips", gives a very detailed description of how to do the measuring, and what in his view is acceptable. As I recall, he was using Federal brass back then, which wouldn't fit the bill today, in my opinion.
I Haven't read Ratigan's version but will see if i can find it and do so.

 

[Mtstalker]

The more i search the more i find that primers and ejector swipe are not reliable pressure indicators or so they say. Obviously if there are ejector marks on the headstamp i back off. But supposedly measuring case heads is a good indicator of pressure?

 

[Langey]

From Hodgdon: Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/rel...-trick-monitoring-pressure-your-rifle-reloads

 

[Mtstalker]

Do you have to use a blade mic or can i use a regular flat anvil one.

 

[jpretle]

Stopp429, if you shave off just enough of the case rim for your mic to clear, at the point you have marked for measuring, you should be able to use the flat anvil mic. All it takes is maybe .001-.002. Set the mic immediately above the extractor groove, no further.

 

[Mtstalker]

Thanks guys.

 

[MagnumManiac]

I have used the case head expansion method before I purchased a pressure trace. The measurement MUST be taken just above the extractor groove on the case. If you don't have a blade micrometer, you can file 2 indexed flat spots on the case rim and use a typical anvil style micrometer. It also needs to read to .0001" accurately, a .001" micrometer shouldn't be used.
Using the standard, as outlined in Speer's #12 manual, I measured just above the extraction cannelure and when .0003" and no more than .0005" expansion was read that was made 'max' for that load. I also took 10 firings on different brass from the same lot that had had one previous firing with a known safe load.

When I tested this on the pressure trace, the results were surprising, not only did some loads with .0005" show excessive pressure, but some showed way under max pressure.
The hardness of the brass is the main factor that governs the amount of expansion. Federal brass I have showed loose pockets with start loads from one manual, while Lapua and Winchester brass showed little expansion until 70,000+psi was reached.
I also noted that it takes a few firings with hard brass to even show ANY exopansion with normal loads, some took 3 firings to expand .003" at a known max pressure load, as indicated by the pressure trace.

If you want your brass to last, regardless of the actual pressure, using the CHE method will keep your brass safe and prolong it's life.

Cheers.

 

[memilanuk]

Something worth reading, if you are going to measure case-head-expansion (CHE):

PRE, CHE, RIP

Some more good reading (from the folks @ RSI)

 

[pdhntr]

Something worth reading, if you are going to measure case-head-expansion (CHE):

PRE, CHE, RIP

Some more good reading (from the folks @ RSI)

Thank you Sir for posting that!

Jim

 

[fguffey]

I also noted that it takes a few firings with hard brass to even show ANY exopansion with normal loads, some took 3 firings to expand .003" at a known max pressure load, as indicated by the pressure trace.

"Some took 3 firings to expand.003"? You said 'normal loads'; with normal loads I would expect the case head to expand .001" for 4 firings. And then I would expect the case head to expand .003" after having been fired 12 times; and then there is the big 'if'. Reloaders believe they can start over by full length sizing and from the beginning I have asked; "HOW?" because the case has been fired at least 5 times, firing a case 5 times work hardens the brass. So, there has to be a point in the life of the case some of this stuff is out the window.

I understand there are reloaders that ooooh and awaaaa about some brands of brass, not me, I do not get silly about brass with tuff case heads, I want my case heads to expand, it takes time for the case head to expand. Expand as opposed to what? A brittle case head can rip open and cause a catastrophic failure.

F. Guffey