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Old February 10, 2013, 05:19 PM   #26
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I find it odd that Lyman back in 1961 and me with six different rifles, one of which is a custom are all out of spec. Look at any manual you want from the 60's and compare it to the manuals of today. The old ones are much hotter than the new ones pretty much across the board. I have an old Hornaday book somewhere I will dig up that has loads that are hot as Hadees compared to what they publish today.
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Old February 10, 2013, 05:28 PM   #27
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Dacaur, Elmer Keith blew up some rifles wildcatting by using too small a starting load. According to him, too small of a powder charge and thus too much empty case space will actually cause a detonation instead of a burn and thus cause an extreme pressure spike for a very short time. Whether that's true or not, I don't know. When I work up loads for a wildcat, I start pretty hot. We developed a wildcat based on the 8mm Rem mag that is slightly edging published loads for .30-378 WBY and doing it with much less case capacity. I'm sure if the reloading manuals got hold of it and published data for it they would knock 300 FPS off it.
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Old February 10, 2013, 05:52 PM   #28
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You can look it up in PO Ackley’s handbook, Mr Speer had so much trouble getting consistent reading from copper crusher pressure equipment that he developed loads without pressure equipment.

In those older manuals “maximum pressures” were determined by examining primers, case head expansion, and difficult extraction. These are unreliable indications of pressure.

Today’s pressure test equipment with piezoelectric transducers instead of copper crushers are as slide rules compared to electronic calculators. Piezoelectric devices are able to read pressure variations’ in real time and to an exact value. Crushed metal discs neither measure pressure in real time nor gave true peak values.

As for design. Rifle mechanisms and brass cases were always designed to withstand a maximum load. This load was a load based on an assumed pressure. Lets say the pressure is 50,000 psia. Safety factors were added on, due to the uncertainty of metal, fabrication, heat treatment, a low fatique life was assumed, and an action built to support that load.

Whenever you have pressures higher than design specifications you are eating into whatever little design margins that were built into the firearm and you are reducing the cycles to metal failure by fatique.

I found this an interesting post on the lifetime of firearms:

Just a few thoughts on this. For Background I am a mechanical engineer with a heavy background in failure and fatigue.

I wonder if I could request a high quality photo of the fracture zone of the cylinder? I am specifically interested in the grain structure of the bolt notches.

I put fort the following.

1) Firearms in general (the type we plebeians can get our mits one) are not designed for infinite fatigue life.

2) The Factors of safety used in firearms design are in line with low end of fatigue requirements (usually less than 10,000 cycles).

3) One of the funny things about fatigue is that each time you push the material past its original design point, you lower its expected life.

4) I am looking at this as an older gun with an unknown number of rounds through it. but based on its age a substantial round count seems likely.

5) When these firearms are designed it is generally preferable for something else to go before the cylinder lets go and takes the top strap. Generally this takes the form of the gun wearing loose or the barrel wearing out. But they are designed to handle X rounds at standard pressures.

6) I see alot of folks calculate the strengths of Rugers, but these calculations are only ever performing an evaluation on a straight static pressure basis. This is wrong when trying to determine if a load is safe.

I attached a couple of marked up figures for your perusal
If I'm not shooting, I'm reloading.
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.308 win , hornady , lee , load conflict

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