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Originally posted by jstevens:
El Deguello
I don't guess I really know what a 7x57 case will hold reliably as far as pressure, so all we can go by is SAAMI specs. I wouldn't be against loading it to the max for a 6mm or 257 Roberts as they obviously use 7x57 brass. The 70000 psi mine registered is too high. My Ruger will handle it, as it's still in one piece and functions fine. I'll still back it off to about 48 grains of H414 and try it then, velocity should drop to a bit over 2700 fps, I'll never know the difference. Another interesting side note is that 48 grains is exactly the Hodgon manual max. listed in a modern Ruger in 7x57 with 154-162 grain bullets at I think 2710 fps.

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Since I have no way of measuring pressures, I must continue to use case life as an indication of what;s acceptable in my rifles, even though "traditional pressure signs" really don't tell us anything definitive. If my brass typically lasts 10 shots or so and the primer pockets are still tight when I seat a new primer, the load is OK for my uses.

My God! I'm with Eldeguelo case life is my indicator but I no longer care if I am getting the last FPS anymore either. I just use a bigger case.

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Originally posted by denton:
Now I spend an hour at the range, and then come home and spend 2 hours analyzing the data. Something has gone horribly wrong.

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Denton, once in a while, a guy just has to leave the pencil, paper, and calculator at home.
Then he can just go out and waste some "wabbits".

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Originally posted by jstevens:
I didn't intend to start a physics discussion, but I do know that if my pressure trace is 6 % off, my highest pressure trace was 74767 psi, so it would still be over 70000 which is 6000 over any SAAMI specs. Case expansion is the same as an old load of 51.5 IMR 4350 with a 140 grain that went 2875 fps.

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I'm still trying to get a handle on the accuracy of Pressure Trace info. My PBL43 instructions say to fire factory loads as they are usually close to max pressure and then don't handload higher than that to be safe. As the 7x57 is old and factory loads are wimpy, I wouldn't think this procedure should apply. Do you have a strain gauge glued onto other barrels where you can compare your handloads to factory loads?

Mr. Stevens -

Your post was interesting in several ways. When I first read it, I was hoping to find some useful information about loads in the 7x57...to perhaps compare with some of my own loads.

I did find some interesting info...
1. Your loads are loaded to a higher pressure than you thought
2. You have never had ANY sort of trouble with those loads, after years of use.
3. You have decided to reduce your loads somewhat, to put them more in line with industry standards.

Your approach to loading seems to be sensible...sort of "If you need more power, use a bigger gun". That is pretty much the kind of approach I believe in also.

After everything else was said and done, I didn't get much more out of the thread - probably because my hobby is shooting and reloading, not the mathematical logic constructs and conventions which make up physics.

The major questions which the whole thread leaves unanswered for me are these: "Why are SAAMI standards sacrosanct?" What are the business, (corporate) political, and belief criteria which led SAAMI to adopt the "pressure levels" it has?" "Why would one feel unsafe using loads which have obviously worked very well in his rifle for years?"

I would use mild loads in any cartridge just because I see no need to use hotter ones. I have this theory that one has less accidents, more product life, and ultimately less cost when they run any heat engine at the optimum rather than an extreme.

But, if I had an engine which ran well on what fuel it had been getting, for many years, I'd probably also feel "If it ain't broke, why fix it?"

Your findings were interesting, though. Thanks for posting them.

Alberta Canuck

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Originally posted by onefunzr2:

I'm still trying to get a handle on the accuracy of Pressure Trace info.

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Me too. My best estimate, considering all of the sources of error that I am aware of, shouldn't be considered definitive, and should be taken with a grain of salt, but right now what I come up with is an accuracy of about plus/minus 2000 psi. That is for pressures in the 60000-70000 psi range, and with the strain gage attached to a suitable barrel -- i.e., one with a sufficiently long cylindrical portion over the chamber. That works out to be about a 3% error, and is just slightly larger than denton's estimate.

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Originally posted by ASS_CLOWN:
Infosponge,

I figured that was the range your were using.

Here is a listing of materials which will cover most firearms.
.
.
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Great! Thanks. You wouldn't happen to also have the Poisson Ratios for these?

Alberta Canuck

I can appreciate your feelings about all the mathematical equations and physics arguments. My interest lies in the practical use of the datat that the presure trace system provides. Obviously this one will function with the loads that I've used for years, maybe I don't have a problem, but I'd still rather back things off a bit, the velocity loss won't be noticeable in field use. In an old article by Jack OConnor, he once said if he had easy extraction, in all weather, case life was 7-1- loadings before the primer pockets loosened up, he didn't care what the pressure was, it was a safe load in his rifle. Maybe he was right, but I'd just as soon allow for a bit of margin for hot weather, etc,

Well, I found some steel data sheets. The data aren't entirely consistent with those ASS_CLOWN provided -- e.g., they list Young's Modulus for 4140 as 29700000 psi, not 29200000 psi. I still haven't got a good Poisson Ratio for 416 stainless.

Using the 2D hoop strain analysis, it looks to me like 4140 results in the least amount of strain compared to 416 and 17-4 stainless (the latter being the stainless that Lothar-Walther uses, while just about everyone else makes their stainless barrels from 416.) 17-4 barrels will show the most strain of these three typical modern barrel steels when loaded with the same chamber pressure. In terms of indicated psi, that means that a Lothar-Walther 17-4 stainless barrel probably will show strain gage readings that are almost 3500 psi too high. (416 barrels probably read too high by about half that amount, but again, I don't have complete data on 416 yet.) In other words, and assuming that the Pressure Trace is setup at the factory to read correctly with 4140 steel, using this strain gage system on a stainless barrel will provide you an additional safety factor of as much as almost 3500 psi -- provided you're not foolish enough to take my word on the 3500 psi difference and then boost your loads by an additional 3500 indicated psi.

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Originally posted by rickt300:
My God! I'm with Eldeguelo case life is my indicator but I no longer care if I am getting the last FPS anymore either. I just use a bigger case.

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Me neither! I learned long ago, while hunting in Alaska, that my .270-cal. 150-grain Noslers at 2750 from a 20" barrel were just as deadly as any other bullet, despite the fact that a lot of others were faster...

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I'm still trying to get a handle on the accuracy of Pressure Trace info. My PBL43 instructions say to fire factory loads as they are usually close to max pressure and then don't handload higher than that to be safe. As the 7x57 is old and factory loads are wimpy, I wouldn't think this procedure should apply.Do you have a strain gauge glued onto other barrels where you can compare your handloads to factory loads?

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Right! there are several others that fall into the "wimp" category as well. Two that come to mind real fast are the 8X57IS, as loaded in the U.S., and .257 Roberts. The .257 R. has never been commercially chambered in a rifle of questionable strength, so it is a real mystery as to why they "wimp-ized" it! The standard factory .30/'06 has always been loaded to a lower pressure than the .270, as has the .280 Rem.!

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The major questions which the whole thread leaves unanswered for me are these: "Why are SAAMI standards sacrosanct?"

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To me, they aren't!!

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"What are the business, (corporate) political, and belief criteria which led SAAMI to adopt the "pressure levels" it has?"

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Supposedly, based on the weakest action in which the caliber might be fired.

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"Why would one feel unsafe using loads which have obviously worked very well in his rifle for years?"

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I don't!!

Got a miserable case of flu... hope this is coherent.

I reload for some calibers that have wimpy book and factory loads... 7.62x54R, 8x57, 6.5x55. In those cases, the pressure measuring equipment is very useful. My 24" Yugo is happily giving me 2750 fps with a 175 grain bullet/55KPSI peak. That's a worthwile improvement.

257 Roberts is usually loaded to low pressure, as are a couple of other US rounds.

You can get perfectly satisfactory '06 loads out of the book, if that's all you need.

Me? I want to know lots and lots about how temperature, powder, primers, etc. work together. So, for me, the technical part of the hobby is the fun of it.