quote:

---

Originally posted by trg:
What about measuring the case with a micrometer.
Like measuring the belt on belted magnums.

---

Hey trg, That is an excellent way to begin measuring First Hand Pressure directly from the case as opposed to some arbitrary, random picked Velocity or Second Hand info from a Strain Gauge. In fact, using a Micrometer to measure the effects of Pressure is the very best and Safest Pressure Detection Method available.

If you decide to go this route, call the Expansion measured across the Belt - Case Head Expansion(CHE). And there is an even better place forward of the Belt to measure the Expansion called Pressure Ring Expansion(PRE).

I like to measure and record both CHE and PRE on my Test Loads. Here are some tips for you:

PRE:

1) You must have a 0.0001" capable Micrometer. A 0.001" capable Caliper just isn't accurate enough.
2) Buy one box of Factory Ammo to establish your Benchmark Standard for PRE.
3) Fire the Factory Ammo and record the value of the widest portion of a fired Case just forward of the Belt(see below).
4) Do this by rotating the Pressure Ring between the anvils of the Micrometer without forcing it to turn. The widest dimension you can measure that will "hang the case" between the anvils is your PRE.

For Example, if 0.52x6" will "hang" between the anvils and 0.52x7" will not "hang", then 0.52x6" is the PRE.

NOTE: This is not the normal way Micrometers are used. But for measuring PRE accurately, this is the way to do it.

5)Average the PRE on all 20 Factory Loaded Cases and record this value as your Benchmark Standard.
6) Always Partial-Full Length Resize or Full Length Resize when doing the Test Loads. DO NOT Neck Size.
7) PRE is good on shots 1 through 6-9 depending upon the strength of the Loads.
8) STOP when a Test Load measures the same PRE as the Benchmark Standard.

CHE:

1) You must have a 0.0001" capable Micrometer. A 0.001" capable Caliper just isn't accurate enough.
2) Do not measure CHE on the initial firing.
3) Always measure the CHE from the exact same spot on the case. Use something in the Headstamp to align with.
4) Always Partial-Full Length Resize or Full Length Resize when doing the Test Loads. DO NOT Neck Size.
5) Reload the fired Factory Case and measure the Belt in one spot. Call this "Before" and record the value.
6) Fire the Test Load and measuring the exact same spot as before, record the "After" value.
7) Subtract the Before from the After and you have the CHE (record this too).
8) CHE is good on shots 2 through 6-9 depending upon the strength of the Loads.
9) STOP when a Load creates 0.0005" CHE.

Those tips will keep you out of Pressure Problems if you follow them.

"Velocity alone" is a pitiful Pressure Indicator because it can be misleading to a person just beginning to reload. For someone who does have some experience reloading and understands why the previous sentence is true, then Velocity can be a useful "additional" Pressure Indicator.

Always use every Pressure Indication Method available to you as you develop Loads from below.

Absolutely no need at all to hose-up a firearm by hanging Strain Gauges on it. However, it is a good way to keep some peoples time occupied, billfolds depleted, reduce the trade value of their firearms, and "BEST OF ALL" it provides you a visual clue to stand well clear of them at the Range.

[ 10-24-2003, 04:30: Message edited by: Hot Core ]

quote:

---

The math is simple. .0005" corresponds to roughly 50,000 PSI, give or take. Your measurements are not going to be any better than .0001", and probably a bit worse. So your resolution limit is somewhere in the neighborhood of 10,000 PSI. That's a full order of magnitude worse that the old CUP method, which is in turn significantly worse than a well-done strain gauge system.

---

quote:

---

Primer appearance, if you KNOW the rifle, can be helpful. If you don't know the rifle, it can be very misleading (it's a good indication of headspace, though!). If you want to measure head case expansion, use once fired brass (in that chamber) of a known hardness. Bolt lift "feel" can likewise be very helpful, or very misleading (especially in factory chambers). Velocity is the most reliable, unless you have something quite wrong (like the wrong size bullet). JMO, Dutch.

---

quote:

---

For decades, I defended the notion of miking cases to get an idea of the internal pressures being developed. I'm the editor who originally published both Bob Hagel's and Ken Waters' articles on how they do it. I also published Waters' "Pet Loads" article as a supplement for his Pet Loads book.
At the time, Waters and I both considered Hagel's method extremely risky. I still do (because it IS!). I supported Waters' more moderate approach. I've since learned how foolish and unreliable any variation of this basic technique is.

� Many cases don't expand enough, even at 80,000 lb/sq in., to warn of risky or excessive pressures.

� Catastrophic failures of overloaded rifles may occur with either the first over-hot round, or they may occur only after years of repeated use of over-hot loads. In the latter type of failure, the rifle has appeared "safe" with these loads, clear up until the time one round "caused" the failure "for no apparent reason."

� Cases work-harden in use. Repeated use makes them become brittle in the crucial portion exposed in the breech � typically 0.200 inch of the head of the case. Cases already too hard to show "excessive" expansion here (some, even at 80,000 lb/sq in.) are especially likely to become brittle in repeated firings and reloadings, and spew wild gas and bits of brass into a shooter's face. I have on hand now a rifle utterly demolished when half the head of the case blew back through the action. The rest of the case is still in the apparently unharmed barrel, but the receiver is in many pieces, and my friend still has one piece of brass in his face (a larger chunk was surgically removed).

� The maximum safe limit for many rifles and cartridges is well below the level of peak pressures that many cases can handle without any discernible or measurable indication of excess.

� The less experienced you are in the use of this method, the greater is the certainty that miking your cases will inevitably lead you to accept dangerously high pressures as "safe."

Careful lab tests of many typical "pet" loads, developed by attention to traditionally accepted "signs" of pressure, have shown their peak pressures to be 70,000 to 75,000 lb/sq in. The highest SAAMI "safe" pressure I know of, for any cartridge or rifle, is 65,000 lb/sq in. Most are lower. Many are much lower.

Some carefully lab-tested loads, developed by miking case rims, webs, and expansion rings, have developed 80,000 lb/sq in. without measurable expansion.

Stay well below the maximum charges listed in the manuals, and you'll be worlds safer without significant sacrifice in down-range performance. No micrometer is a reliable pressure gauge.

And being immensely privileged to be privy to a lot of factual findings -- both classic and recent -- about interior ballistics, factual material that hasn't found its way into the gun magazines and isn't obvious enough that every opiner in print or cyberspace sees its validity at first glance, I feel duty-bound to share the impact of these facts even though such sharing inspires onslaughts of doubts and dissenting opinions. It's worth noting, IMO, that none of these doubts or dissenting opinions comes from a dependable, well equipped experimenter who has tested and examined the validity of case expansion with good pressure-measuring equipment.

When several careful and dependable experimenters, each well equipped and confirming the others' findings, report that miking case expansion to "read" pressure has in their experience produced two significant bodies of serious error, I take all that as observed fact, not conjecture or opinion.

Those two bodies of repeatedly observed error are --
(a) case-expansion readings that indicate dangerously high pressures, when the pressure guns indicate pressures well below maximums
and
(b) case-expansion readings that DON'T indicate excessive pressures, when the pressure guns indicate pressures at AND ABOVE proof-load levels -- DANGEROUS loads that case-expansion readings do NOT detect, for example 70,000, 75,000, even 90,000 lb/sq in. in cartridges SAAMI-rated at safe only below 60,000 lb/sq in.

So my opinion of case expansion's worth doesn't matter. The facts do matter. And I don't have to have discovered those facts myself. Also, my acceptance of these facts isn't determined or affected by the dissenting opinions of otherwise well informed and intelligent people who happen NOT to have learned these same facts.

So my opinion is that the statement "Case expansion is a dangerously misleading and undependable method of trying to 'read' peak chamber pressures" is a well and repeatedly proven fact, based on well and repeatedly proven facts (not opinions based on old, opinion-based writings). I also opine with some confidence that this opinion is sturdily supported by enough repeatedly observed facts to qualify it as a final opinion.

---

quote:

---

I just did a bunch of the same research, and came to the same conclusions, by shooting loads worked up with "home" pressure testing methods (from bolt lift to measuring case heads) in a professional pressure lab. Could find no consistent correlation between case expansion (or even bolt lift!) and pressure. An article will appear in the next HANDLOADER on the experiments--which will also corroborate Blaine's contention that a chronograph is the best indicator of pressure.

---

quote:

---

Originally posted by denton:
T/C...

Your point that the brass does not start to stretch until some critical pressure is reached is a good one. Practically all the stretch will occur at the peak pressure, and it may be non-linear, ans you've said.

---

quote:

---

Originally posted by Rev howl:
Some carefully lab-tested loads, developed by miking case rims, webs, and expansion rings, have developed 80,000 lb/sq in. without measurable expansion....

---

quote:

---

Originally posted by howl:
I also opine with some confidence that this opinion is sturdily supported by enough repeatedly observed facts to qualify it as a final opinion...

---

Oh yes, no need to "disagree" because the Rev howl has decided his opinion is final.

quote:

---

Originally posted by denton:
I have not done the formal analysis of the CHE method, and cannot tell you what its limits are. In my case, I just did some preliminary noodling (explained above), and decided that the method wasn't very promising. So I haven't done the investigation on it....

---

Hey Denton, Now there is an interesting quote which seems out of place for you. You admit you've never done a formal analysis on CHE(and totally avoided PRE) and yet decided, "that the method wasn't very promising."

Are you studying under howl or did you get some Strain Gauge wires hung around your neck and cut off the blood to your brain? Speak up, which one is it!

quote:

---

originally posted by Brent:
How much confidence does Hot Core have in this method while not knowing anything about the loads? The way he talks he don't need to know nothing but a starting point, a true blind test at it's best...

---

quote:

---

originally posted by Brent:
...when someone learns all the facts about something that's the logical progression don't ya think??? Do I have to give examples???...

---

You've mentioned a couple of times in previous Threads you were planning to try PRE and CHE for yourself. But, it appears you still haven't tried them. Am I wrong? Let's assume that I am wrong and you did try PRE and CHE as I originally outlined. Yes indeed, I am interested in the "examples" you just mentioned. What did you see??

With that in mind and knowing you would not be one of the "fools" to criticize something you've never tried, how did your results come out? Did you follow the instructions as I posted above or try something different that can skew the results?

The good part about this, is I'll believe your response. I don't believe you would intentionally misrepresent what you actually saw, so what was it??? If it is in fact some value that looks improper, I should be able to help you figure out what is going wrong without you having to mail me a thing. Nor will you need to buy extra glue, wires or a larger truck to haul all the stuff to the Range.

[ 10-27-2003, 16:52: Message edited by: Hot Core ]

quote:

---

Sounds like a perfect test to me!!!! And about time there's a step to resolve this never ending dispute... Let the chips fall where they may.

---

quote:

---

Originally posted by Dutch:
Hot Core, maybe you didn't quite understand the post.

Your last post could have been written by the good Rev.

You are convinced your method is better. Prove it!...

---

Hey Dutch, I must be missing the point as you say. It seems to me anyone should be able to do the Test without my interference. I've already said I'd believe Denton's and Brent's results. That will "prove it" without anyone thinking I skewed the results.

Heck, I'd even believe "your" results if you care to post them. No need to hose-up the data with a bunch of worthless Velocity info either.

Getting a bit testy with that comment about Rev howl? I know you didn't mean it. Let me guess it is because you've also never tried doing PRE or CHE as outlined above. Surely you aren't one to criticize a Method you've never properly tried.

I can see why you would be frustrated when a good old set of RCBS 0.0001" capable Micrometers from www.wideners.com for $21 will give you SAFER, more accurate, First Hand Pressure Data directly from the weakest link in the Firing Sequence.

quote:

---

Originally posted by T/C nimrod:
[QUOTE]It's the dicussion that keeps minds open.

Lets not lose tract of how this CHE process is to work either. Unless I'm mistaken, You need a baseline to work with. ...I guess my question at this point is: Is pressure/case expansion equal within a set of boundaries?

In other words, say you have a 180 grain .30-06 factory load that measures .0045" CHE. say this correlates to 60,000psi (I don't know that pressure is right, I just used that number for example purposes). Now, while shooting a ramp of handloads (different powder/primer/bullet combo), we are saying that a load that shows .0045" expansion won't be in the ballpark of that original 60,000psi?

Then, what if the velocity were put into play?

---