Home Forums Hunting & Shooting Ask The Gunwriters Safe Pressures?

Thanks, Buford.

I found the comments on my primer-appearance article interesting as well. Quite a few people didn't want to believe fired primers aren't the equivalent of pressure-testing.

And I seem to recall one or two questioned General Hatcher's qualificationsl. All he ever did was graduate from the United States Naval Academy in Annapolis, then transfer to the Army, where from 1917 to 1945 he served as the:

Officer in Charge, Experimental Department, Springfield Armory
Chief of Machine Gun and Small Arms Section. Engineering Division, Ordnance, Washington D.C.
Works Manager, Springfield Armory
Officer in Charge of Small Arms Ammunition Manufacturing, Frankford Arsenal
Chief of Small Arms Division, Manufacturing Service, Ordnance Department, Washington D.C.
Assistant Commander, The Ordnance Training Center
Chief of OrdnanceTraining Service
Chief of Field Service

The last two assignments were during World War II, from 1941-45.

After retiring from the Army, he became the Technical Editor of American Rifleman magazine, back when it was far more technical than today. He knew a thing or two about arms and ammunition.

It's prudent to check sources, isn't it?

Metal fatigue is indeed cumulative, yet when metal lets go it is sudden and mostly without warning

YEP!!!!

Quite a few years back I typed out part of a chapter from the book, PRINCPLES OF LOADING AMMUNITION by Earl Narramore. He went into some detail about a rifle using hot loads "stored energy", what I believe his meaning being metal fatigue. I don't remember if it was here or on another site but I got flamed pretty badly. I still think Mr. Naramore was right. I also think that before anyone reloads a single cartridge that they should read his book. JMHO.
Paul B.

Looking at the OP's pictures it seems that both cartridges show slight cratering. I'm not all that sure that it's meaningful. I gave a Remington M700 BDL that will give cratered primers with loads as soft as 5.0 gr. of Unique and a 115 gr. cast bullet. I know the charges were correct but why???? Upon inspecting the bolt, I noticed the firing pin hole looks as if it has been chamfered slightly. As I bought the rifle brand new i the box, it had to have come from the factory that way. Every load I shoot in that rifle, be it very light gallery loads or a full power level hunting load, I get a cratered primer. BTW, the rifle is a 30-06.

As far as that primer on the OP's left hand cartridge, that wouldn't have bothered me all that much. Looks like the primers on my top .35 Whelen load and brass life for that cartridge has been very good. I've seen too many factory loaded cartridges that produced flattened primers that looked like top hats. WTF?????
Paul B.

Regarding the flat primers, I recall visiting the pressure test facility of a major ammo company many years ago. After watching a routine test (back in the days of copper crushers), my host handed me a few of the fired cases. He asked, "What do you think?" The primer was flattened all the way to the brass. With all my wisdom I intoned that, "The primers sure are flat; pressure must be way up there." He replied, "No, actually the pressure is lower than usual. The firing pin drives the case forward, the primer backs out shortly after ignition, then the pressure drives the case back against the bolt and the protruding primer gets smashed. Happens all the time with the .35 Remington and its small shoulder. We just call it a "nailhead"."

So ended my faith in reading primers.

Buford verified the same process in his video.

Excellent post - pretty much sums up the whole issue.

I certainly don't have the expertise as some on this thread, but have used an Oehler 43 for 20 years. It has been an enlightening experience. I don't have access to "reference" loads, so just test a variety of factory loads to give me an idea of factory pressures and also to provide an indication that my pressure readings are close. I found that some of my not maximum loads tested over 70,000 psi. with no indication of higher pressure.

That isn't quite how metal fatigue works. In fact "fatigue" is a really misleading name for it, from a time when the mechanism wasn't well understood.

With a fatigue failure, what actually happens is that a crack starts, usually at some stress concentration such as a sharp corner, inclusion, machining mark or something like that. Under repeated load cycles - the number depending on factors like how close the load is to the ultimate tensile strength of the material, but usually we are talking in the thousands or more load cycles - the crack gradually proceeds to get longer. Eventually the remaining cross section isn't enough to support the applied load, and the part fails. The fracture surface, as a result, has a really distinctive appearance - you can usually see where the crack started, and the gradual progression looks like a beach after the tide's gone out. You then see the distinctly-different part of the fracture where the overload finally saw it let go. You can usually determine a lot more too, such as the nature of the load (eg simple bending vs reversed bending vs torsion etc) and whether it was low load high cycle or high load low cycle to failure.

Under constant cyclic loading conditions you can also not only look for but also monitor fatigue cracks, and only act when they are getting to a critical length. This is often the case in aircraft, where a crack may be monitored rather than the part immediately being replaced. Fatigue failure is not really something that happens "without warning", if you know what to look for.

You can also reduce the likelihood by such things as your choice of material and design, but also paying careful attention to things like surface quality, defect free material and use of generously-radiused corners.

The loading conditions of sporting rifles really aren't highly likely to give rise to fatigue failure. Rifle actions undergo comparatively few load cycles over their lifetime, and are typically working at a small fraction of UTS. Yes, you could (at least in theory) increase the likelihood of fatigue cracks with a diet of hot loads and a lot of them, but the failures you do tend to see are typically simple overload, associated with something like a pressure excursion. Your worst case is a pressure excursion coupled with a brittle receiver, cos that is where bits start flying around.

And when it fails, it is: