Re: 3030 Ackley Pressure Ring Measurements

27 June 2004, 01:19

Hot Core

Hey Deke, I thought someone else might help you, but since they haven't I will be glad to. However, I'll do it via email or phone since the way to do this could get a Beginner reading this in over his head rather quickly.

One thing that will help is for you to read the thread AC started where he discussed why Case Head Expansion(CHE) won't work on most "Rimmed" cartridges. Even thought you are using a Marlin, you sure don't want to get to the Pressure Level where CHE occurrs.

I just copied down your email and will send you a message as soon as Hotmail will let me. When I tried to sign in to it earlier today, it was down. Meanwhile it will give me a chance to look through some old stuff of mine and see if I have anything saved on Improved 30-30s.

Pressure Ring Expansion(PRE) will be a help to you, but it is not as straight forward as when you have a Standard cartridge.

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Quote:

. Does the AI reamer change the factory chamber at the pressure ring (hard to tell from drawings @ Steve's pages)? If it does not then I have a baseline to start with. If it does then I really have no way of establishing a factory baseline since the chamber is now bigger and the pressure and pressure ring measurements will be less w/factory ammo....

The big problem here is it "might" have changed. Had you thought through where you are right now, then the problem could have been addressed in the beginning and you would know for sure. That would have required some measurements with a CMM before and after chambering, which would have told you for sure.

Even asking the GunSmith who did the rechambering might not tell you much. He could say if he moved the barrel back one thread(which is normal) and that would indicate the entire chamber has been recut. If however he did not move the barrel back a thread and the cutter was designed to "only change the shoulder angle"(I kind of doubt this) then your original PRE data would be useful to you.

Some of the Improved cases only change the Shoulder angle and some also straighten the Case walls slightly. And of course, that would change the Chamber dimension at the Pressure Ring.

Anyway, you will hear from me once Hotmail gets going.

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Just tried Hotmail at 8:30AM EST and can't get in. It will be later this afternoon before I try again, but they will eventually get it up and running.

01 July 2004, 02:07

irv

One thing should be kept in mind; When the case head shows expansion it has been taken beyond it's elastic limit.
For that brass & load in that chamber it is time to stop and think.
Take Care!

02 July 2004, 02:19

Hot Core

Hey Deke, That is excellent news indeed. I totally agree with your approach and intended use for the rifle.

Best of luck with it. And I also agree it would be nice if anyone cared to share a few more ideas with you. I'm always interested in learning something new..... that works.

Once you do get it going, kick this Thread back up and let us all know how well it is doing.

02 July 2004, 05:08

denton

Quote:

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... the different manufactured 3006 ammo producing very different pressures ...

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Yes indeed. That is "WHY" standard factory ammo can't be used to Calibrate a HSGS.

Hot Core is the only person I know that has suggested that you use factory ammo to calibrate a strain gage system. I certainly never have. Here, he clearly tells us why it won't work.

Then, again, he tells us that it does work for PRE.

Quote:

PRE would work "IF" the Chamber had not been cleaned up and set back a thread, because he could have used the Factory Loads shot in the original Chamber to establish a Standard.

So which is it, Hot Core? You can't have it both ways.

02 July 2004, 05:44

denton

Quote:

As I said, several ballistics labs (such as H.P. White) have conducted tests in which it was discovered that rounds showing higher pressures with pressure testing equipment produced LESS case expansion than rounds that showed a lot less pressure. This with EVERY VARIABLE being identical. Cases, bullets, powder and primers from the same lot, same powder charge, etc.

I did the same thing, and got the same result. I fired matched pairs of cartridges, and miked them with a .00005" resolution Mitutoyo electronic micrometer. And I did test it before I used it. It does have the advertised resolution.

Result: 39% of the variation in pressure ring size came from pressure, and 61% was random noise, using a baseline of pressures that spanned 30,000 PSI. If you try it on a 10,000 PSI baseline, the results will be much less favorable.

All the experiments that I know of confirm this result. I know of no experiments that show the opposite. To the best of my knowledge, Ken Waters never performed an experiment to support his opinion.

It would be very handy if PRE worked. I wish it did.

Deke, if you're curious, you can replicate the experiment. Here are the instructions.

Prepare at least six to eight matched pairs of cartridges (I did 14). Make them all with the same powder, primer, case, and bullet. Make the hottest load about what you think will be safe maximum, and make loads at half grain (or quarter grain if you prefer) intervals from there down. Label your cases with a Sharpie pen.

When you shoot them, shoot about three fairly mild cartridges to bring the barrel up to temperature. Space your shots out so the temperature of the barrel stays constant. Constant barrel temperature is VERY important. Barrel temperature is a major pressure factor, and if you don't control it, you'll get extra pressure from your later loads. Barrel temperature is easiest to control very early in the day, when it is relatively cool. Failure to control barrel temperature will seriously corrupt the experiment, unless you fully randomize.

From a statistics standpoint, it is best to randomize the order of firing the matched pairs. From a safety standpoint, it is best to work up from the bottom. If you safely can, mix the order up a little bit (I have no sense, and fully randomized.). When you get done, set up a graph with grains of powder on the horizontal axis, and pressure ring diameter on the vertical axis. Plot your data.

Unless it is your lucky day, you will find hot loads that produce less expansion than mild ones, and vice versa. You will find that that the upward trend line in the data is there, but swamped with random noise.

You won't need any statistics. Your graph will tell you the story. When you get done, ask yourself how much confidence you have in a "standard" derived this way, from factory loads.

Don't take my word for it. Do your own test. Or, if you prefer, take Hot Core's word that PRE works. It's a free country, and the rifle is yours, after all.