Carteach is in the process of load development for Liberty, the M1 Garand. This entails shooting... lots and lots of shooting... but that's only part of the happiness. It also requires lots of hours blissfully spent at the reloading bench.
Part of the process involves case preparation. On this topic, books have been written... but not by The Fat Man. Here, just one small topic is being addressed.
In choosing which cases to run the load development with, the entire 30-06 inventory in play. That means over 1000 cases of different date and manufacture. Amongst them, a fair number of military casings.
The thing is, there is a 'Given' in the reloading world. It's been engraved in stone for so many generations that it's accepted as a golden rule. That is: Military brass is thicker and heavier than commercial brass. That means the interior volume of the case is smaller, so therefor the charge weight must be lowered or excessive pressures will result.
But.... is this rule so golden?
Today Carteach took a bullet for the team, and weighed several hundred cases, both commercial and military. The results were unexpected. Weighing the cases is a traditional way of separating out cases into lots of like-volume. The theory being that all sized cases have outside dimensions pretty much the same, so any weight variations must point towards differing case thickness, and thus differing internal volume. (As one intelligent reader pointed out to The Fat Man... metal density comes into play as well. He proposed a simple test for internal volume, consisting of filling the cases with water before weighing them. This makes sense, as the weight on the water filling the case will vary depending on internal volume of the case. This sounds like a wonderful excuse for further testing, and another article here....)
The bulk of the cases were divided into three major types. Greek HXP, Lake City, and Commercial Remington and/or Federal.
Here's the unusual part.... on average, the commercial brass was heavier than all the military. Both Lake City and the commercial were heavier than the Greek HXP military. This indicates the HXP does not have a smaller internal volume, but in fact has a larger one. This changes the whole ball game when loading with the Greek HXP brass.
That chart below shows a clearer picture of what was found:
Now, I know this isn't exactly going to be wildly interesting for those not deep into the intricacies of hand loading.... but for those us who share that particular addiction, it's fascinating.
9 comments:
'Teach;
When I did my testing, first with a balance beam scale & then much later with a digital scale, (what an improvement!) My results mirrored yours. Federal on average was the heaviest(& had the highest std deviation), RP & HXP were nearly the same (& had the smallest std. deviation), Winchester the lightest. Lakes City was in the middle. Interesting that the same relationship held for .308 brass. With .308 however Hornady brass was by FAR the lightest.
Best of luck with your new employer. These things generally work out for the best.
Roger
Carteach, since I know that your blog is as close to a peer reviewed journal as you can get (LOL) here is my input...
Just one other factor to determine. The density/composition of the case material. Herein lies the tricky part. Again "we" need some water ! You'll have to remember all your HS Chem stuff about Archimedes, specific gravity etc. LOL....
I suggest the following:
One tall and thin metric graduated cylinder - like these - http://www.indigo.com/glass/gphglass/graduated-cylinder.html
Various cases WITHOUT a primer (I would tumble them also to get any material cleaned out from the interior)
Insert and measure the displacement of the case. Be consistent with the water line. There are two lines called the meniscus. An upper and a lower line.
http://chemistry.about.com/od/chemistrylabexperiments/qt/meniscus.htm
Now divide the weight by the displacement to get the density of the material as a weight per Cubic Centimeter.
https://en.wikipedia.org/wiki/Displacement_%28fluid%29
http://wiki.answers.com/Q/How_can_water_displacement_be_used_to_measure_the_density_of_an_irregularly_shaped_solid
I bet you may see differences between the brands.
LIM.... Very interesting idea, and of course I have exactly the right graduated beaker out in the shop (Doesn't everyone?). I use it for measuring specific gravity of fuel, but it will do fine for this.
This is interesting since I had heard the story that the Hellenic Defense Industries (HXP) production line was set up by Winchester, to commercial standards.
Have you tried measuring the internal volume of a sample of your cases using water? I think that would give you a better idea of what you're dealing with.
Holy Smoke! I actually performed this exact test yesterday and Monday - and with pretty much exactly the same results. I have a quantity of HXP dated from '67 to '70, and up until recently, this was the vast majority of my '06 brass. But a recent range windfall added a number of R-P headstamps to the pile, so I thought I would weight a few and see what was up. To my astonishment, the R-P matched your figures - 10+ grains heavier across the board. I also found a small group of '68 HXP that was about 12 grains lighter than the rest - with no visible difference (all cases had been cleaned, de-capped and trimmed).
I did have exactly one Winchester case, and it was very light - about the same as the light HXP, and more than 20 grains lighter than the R-P.
I don't have enough LC to make a test, but I do have a small pile of WW2 brass - mostly TW & DEN, IIRC. I need to dig those out and see where they fall..:-)
I'm very suspicious of the similar trending of the commercial and LC weights through the 5th weighing.
Your test bears repeating and the trend needs to be explained - some kind of balance error? Does the balance need more warmup time (if its electronic)? What order were the weighings done in?
Dubya Bee
WB..
The samples were actually far larger, over thirty pieces each. I was just too lazy to graph them all. The pieces were weighed randomly as I sorted, and any cases that pushed the envelope had the scale re-zeroed and got weighed again.
Nothing here is really scientific. I don't even play a scientists on tv.
I went back and weighed my small bucket of "old military other than HXP", and I found that, just as you did, LC ('53 and '54) was a couple grains heavier than the HXP, while the TW ('43, '53 & '54) was a touch lighter, maybe 2-3 grains.
So NONE of my military brass was as heavy as the R-P, though pretty much all of it was heavier than the lone Winchester case I have. Maybe whoever sourced that bit about military being heavier was looking at Winchester.
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