Telling high pressure sings

07 February 2004, 16:06

I have read 5 or 6 different was of how to tell high pressure sings by checking the case after shooting it.One way was to measure head of case it should not be more than .002..Does this mean the inside of the head or out side and where on head do you measure? Also what are some other sings that
i could check for on a fired case?
Thanks ANTHONY

07 February 2004, 16:14

denton

You're likely to get a lot of responses on this. It is a very emotional issue to some.

There are those who claim that the case head expansion method, and the case head expansion method work well. Waters was an advocate of the system.

There are others who claim that it is dangerous. Howell, another respected writer, is one who claims it is dangerous.

I'm in the middle of a test to find out. At the moment, I'm very skeptical of the methods, but the data will eventually tell.

07 February 2004, 16:43

Sabot

Denton is right, the advice you get on this will be emotional and all over the map. All I can offer is that a chronograph is a big help, as you can use it to see what your own guns tendencies are by comparing published loads and velocities with the way they perform in your firearm. Most likely your "duplication" loads will be faster or slower than the book says. This trend will show up while yopu are working up from reduced to max loads.

If you gun shoots slow, don't exceed the max charge without actual pressure testing equipment. If your gun shoots fast, don't go faster than the max velocity listed for that combo of components.

07 February 2004, 16:44

Clark

With my dial calipers I can resolve .0002" of extractor groove growth, but often I see .010". The .0002" will be from a load a couple grains less.

Anyway, I like to reduce the load by 6% from the tiny change in extractor groove.

Example:
257 Roberts Ackley Improved VZ24, Lother Walthar barrel
75 gr. Vmax .257 bullets that I had moly coated.

1) 49.4 gr. of IMR4895, 3942 fps, the extractor cut grows .0035"

2) 48.3 gr. gives 3757 fps and the extractor groove grows .0005"

3) 47.2 gr. gives 3736 fps and no extractor groove growth

4) 45 gr. gives 3674, 3621, 3630, 3614, and 3630 fps

The lowest load with any change is 48.3, so 94% of that is 45.4 gr. I was not at the bottom of my resolution, but rather than search for it, I assumed it was very close and took 45 gr as the max load for sustained term use with long brass life and very low probablity of a stuck bolt at the wrong time.

08 February 2004, 04:38

Hot Core

Quote:

...where on head do you measure? Also what are some other sings that
i could check for on a fired case?...

Hey ANTHONY, Gotta disagree with anything at all being "emotional" about measuring the Expansion of Cases. It has provided an excellent method of Pressure Indications for well over 100 years. And the best part is, it will continue to do so long after we are all gone.

First off, there is Case Head Expansion(CHE) and Pressure Ring Expansion(PRE). PRE works on every cartridge fired including low pressure 38SPLs, 30-30s,etc. The CHE won't work on some of the lower pressure cartridges because the SAAMI MAX Pressure for them is below the pressure necessary to cause the CHE.

You do need a set of 0.0001" capable Micrometers which are available from www.wideners.com where a couple of styles are listed. The $21 set from RCBS will do everything you want, or check with a Pawn Shop near you to see if you can get a bargain. I got my Thin Blade Micrometers at a Pawn Shop for $25 and they work great.

Since Clark answered the first part of your question, I'll answer the second part with a "cut and past" from a previous thread:

The best way I've found to insure a correct reading is to measure the Casehead prior to Firing in one specific spot (say directly opposite the "P" in R-P), record that measurement to 0.xxxx", fire the case, remeasure across the "P", record that value as 0.yyyy", then subtract getting 0.000z" CHE.

Additionally, no one to my knowledge has ever said or even suggested a person can base CHE on the results of only one case. It should be taken using one Load on at least three cases from the same Lot and 4-5 if practicle. At that point, you would "Average" the CHE and compare it to the original (average) Benchmark Standard CHE derived from a box of factory ammo (10-20 cartridges).

PRE is totally different. You measure it only "After Firing" and you do rotate the Case until you locate the "high spot" on the Pressure Ring. Then you record that data and compare that PRE directly to the (average) Benchmark Standard PRE.

In either method, measuring CHE/PRE should only be done for 6-9 reloads which varies due to the intensity of those specific reloads. After that point, the Cases "work-harden" and the CHE/PRE values are suspect. If the Primer Pockets are still snug, they can still be used for regular shooting practice.

And, the reloader must either Full Length Resize(FLR) or Partial-Full Length Resize(P-FLR) in order for the Pressure Ring to be reformed back into the Casewall between Firings while doing PRE measurements. Do not Neck Size.

The bottom line is, everything I've posted about CHE/PRE is verifiable by anyone who has a set of 0.0001" capable Micrometers. No "emotion" at all to it.

...

There are other Pressure Indicators such as a Sticky Bolt Lift, Loose Primer Pockets, Shortening of the Primer Pocket Depth and these all occur "AFTER" you have gone beyond the SAFE MAX Load for that specific Lot of cases. Use a different Lot and you may need less Powder(or more) to reach those same - excess Pressures.

Flattened Primers "may" indicate Pressure too high, but it can also indicate Pressure too low "IF" you are not Partial-Full Length Resizing your cases. This is because when you Full Length Resize, you can induce a bit of excess headspace and the Primer get "riveted" during the firing sequence.

The various Reloading Manuals from the Bullet and Powder Manufacturers are excellent sources of information. If you don't have 3-4 of them, I'd encourage you to buy them. I can see 10 from where I'm sitting right now and have more scattered about the house. They should be used as "Guidlines Only" and not Bibles. A particular firearm may be able to use Loads listed in them,and then again, they may be too high for your firearm and unique set of components.

Use every Pressure Detection Method available to you, use them all with caution and you will do just fine.