Privi Match and Federal GMM brass and capacity ?

alloy · June 14, 2010, 05:02 PM

Any personal methods to check these cases for capacity, I have a stash I want to reload, not sure if they are military type capacity like LC, or more like commercial...

So any how-to's to check case capacity? Resize, fill with water, spent primer to plug the hole, and weigh the water?

Or am I off on the wrong track, out in left field here?

**Unclenick** · June 14, 2010, 06:09 PM

If you are planning to use QuickLOAD or other internal ballistics software, the capacity of the cases as fired (not resized) in your chamber is what you want. Pick one that's got average brass weight for the lot. Weigh it empty and again with water filled to the mouth flat (no meniscus). Subract the brass weight to get water capacity in grains. Record the length to use with the capacity measurement in the software.

If you want to know whether the cases are more like past military cases you have or more like some commercial you have, just weigh them. Matching weight is going to be close to matching capacity, as the outside dimensions are similar, whether sized or fired in your chamber. 70:30 brass has a density of 8.53 grams/cc, so divide the weight differences in grains between any two cases by 8.53 to get the approximate difference in water capacity.

SL1 · June 14, 2010, 06:18 PM

When you measure water capacity, do it with a case that has been fired in YOUR gun and has NOT been resized. Leave the spent primer in so that the water doesn't leak out. Weigh the empty case. Then, fill it with water so that it is FLUSH across the mouth and weigh it again. The difference is the case capacity in "grains of water" which is the standard of measure in the U.S.

To get the water flush across the case mouth, use an eye dropper to fill the case and over-fill it a little at first, so that the edges of the case mouth get wetted. Then use the eye dropper to suck just a little water back out of the case so that the water surface across the mouth is flat. You can use a reflection of a light with a straight edge, like a window of florescent bulb, to check for a flat water surface; when the reflection is also straight, then the water surface is flat instead of bowed in or out.

It is easiest to weigh the long rifle cases on an electonic scale. On a balance beam scale, the pan hanger gets in the way of keeping the case upright. If all you have is a balance beam scale, then you can easily make a special hanger for weighing your cases when they are filled with water. Just take a piece of stiff wire, like maybe 14 gauge electrical wire (stripped) and twist it in a loose spiral around a dowel that is somewhat larger in diameter than your case. On one end, bend the wire so that it goes straight along the dowel instead of spiraling, then when the dowel is removed, bend that part of the wires so that it becomes a hanger that clears the case easily but ends-up with a hook that attaches to the loop on the end of your balance beam. On the other end, bend a short piece of the wire directly across the end of the spiral to serve as the "bottom" of your basket. To keep this shell basket from hitting the table that the scale is sitting on, place the scale near the edge of the table and let the basket hang over the side.

SL1

alloy · June 14, 2010, 06:50 PM

Super, thanks SL1 and Unclenick, I must have been wandering when I was going to pour the water in the pan to weigh it. Weighing the case dry and full seems a more advanced technique.

Quote:

If you want to know whether the cases are more like past military cases you have or more like some commercial you have, just weigh them.

Yes that's what I'm after ultimately, but I might as well set a method. Not bench shooting or even having a rifle that accurate...right now it's more or less just which of several buckets to throw the cases into....but one day it will come in handy to know and be set up with an eydropper.

Come to think of it I have a few other cases to check.

alloy · June 14, 2010, 06:53 PM

Bookmarked.

June 14, 2010, 06:09 PM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,118	If you are planning to use QuickLOAD or other internal ballistics software, the capacity of the cases as fired (not resized) in your chamber is what you want. Pick one that's got average brass weight for the lot. Weigh it empty and again with water filled to the mouth flat (no meniscus). Subract the brass weight to get water capacity in grains. Record the length to use with the capacity measurement in the software. If you want to know whether the cases are more like past military cases you have or more like some commercial you have, just weigh them. Matching weight is going to be close to matching capacity, as the outside dimensions are similar, whether sized or fired in your chamber. 70:30 brass has a density of 8.53 grams/cc, so divide the weight differences in grains between any two cases by 8.53 to get the approximate difference in water capacity. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

June 14, 2010, 06:18 PM	#3
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	When you measure water capacity, do it with a case that has been fired in YOUR gun and has NOT been resized. Leave the spent primer in so that the water doesn't leak out. Weigh the empty case. Then, fill it with water so that it is FLUSH across the mouth and weigh it again. The difference is the case capacity in "grains of water" which is the standard of measure in the U.S. To get the water flush across the case mouth, use an eye dropper to fill the case and over-fill it a little at first, so that the edges of the case mouth get wetted. Then use the eye dropper to suck just a little water back out of the case so that the water surface across the mouth is flat. You can use a reflection of a light with a straight edge, like a window of florescent bulb, to check for a flat water surface; when the reflection is also straight, then the water surface is flat instead of bowed in or out. It is easiest to weigh the long rifle cases on an electonic scale. On a balance beam scale, the pan hanger gets in the way of keeping the case upright. If all you have is a balance beam scale, then you can easily make a special hanger for weighing your cases when they are filled with water. Just take a piece of stiff wire, like maybe 14 gauge electrical wire (stripped) and twist it in a loose spiral around a dowel that is somewhat larger in diameter than your case. On one end, bend the wire so that it goes straight along the dowel instead of spiraling, then when the dowel is removed, bend that part of the wires so that it becomes a hanger that clears the case easily but ends-up with a hook that attaches to the loop on the end of your balance beam. On the other end, bend a short piece of the wire directly across the end of the spiral to serve as the "bottom" of your basket. To keep this shell basket from hitting the table that the scale is sitting on, place the scale near the edge of the table and let the basket hang over the side. SL1