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amamnn · October 24, 2006, 01:47 AM

Depending upon the degree of accuracy you are going for, you may want to check case volume rather than weight. There can be quite a surprising difference in the actual capacity of cases that weigh nearly the same and believe it or not, you can actually find heavier cases that have more volume than some lighter cases. This variance is most pronounced in new, non-premium brass and can be a problem with neck sized brass, especially if the chamber of the rifle where fireforming is done is a bit loose and brass rebound is not controlled. We're not talking huge differences, but it's something benchrest and long distance varmint shooters obsess about.

When I was first informed of this apparent paradox, I did not believe it, but I checked a dozen LC .223 rem cases that all weighed within .1 grains of each other. I filled them all up with water, using a small syringe, emptied them into a powder pan and weighed the water. Mostly, the capacities all weighed out within .1 grain of each other, but I had one that was .5 grain heavy, a pretty big variance in a small bore round. Since then, I sort my cases by weight, but I also check the volume, using clean fine grained sand. Every now and then I get a surprise and cull it, even with Lapua or Nosler brass. Full length sizing and careful control of the head to shoulder length and neck length helps a lot. Since using this method, I've cut down on mysterious flyers.

I'm told that the reason that you can get odd volumes is because of variations in case wall thickness and the relation of the head thickness to wall thickness. Cases can be made with a heavy head and thin wall as you approach the shoulder and vice versa, which affects the volume noticably when compared with a "normal" case. New or neck sized brass may not have shoulders set at exactly the same length. A case with a short shoulder and a long neck may have a smaller volume than a heavier case with a shorter neck. Again, these are small differences, but the various small variations can add up to the difference between first and third place in a match.

Most shooters will probably not need to worry about these little details, but those who want to shave 1/8 MOA or so might be interested.

October 24, 2006, 01:47 AM	#6
amamnn Senior Member Join Date: May 13, 2006 Location: WA, the left armpit of the USA Posts: 1,323	Depending upon the degree of accuracy you are going for, you may want to check case volume rather than weight. There can be quite a surprising difference in the actual capacity of cases that weigh nearly the same and believe it or not, you can actually find heavier cases that have more volume than some lighter cases. This variance is most pronounced in new, non-premium brass and can be a problem with neck sized brass, especially if the chamber of the rifle where fireforming is done is a bit loose and brass rebound is not controlled. We're not talking huge differences, but it's something benchrest and long distance varmint shooters obsess about. When I was first informed of this apparent paradox, I did not believe it, but I checked a dozen LC .223 rem cases that all weighed within .1 grains of each other. I filled them all up with water, using a small syringe, emptied them into a powder pan and weighed the water. Mostly, the capacities all weighed out within .1 grain of each other, but I had one that was .5 grain heavy, a pretty big variance in a small bore round. Since then, I sort my cases by weight, but I also check the volume, using clean fine grained sand. Every now and then I get a surprise and cull it, even with Lapua or Nosler brass. Full length sizing and careful control of the head to shoulder length and neck length helps a lot. Since using this method, I've cut down on mysterious flyers. I'm told that the reason that you can get odd volumes is because of variations in case wall thickness and the relation of the head thickness to wall thickness. Cases can be made with a heavy head and thin wall as you approach the shoulder and vice versa, which affects the volume noticably when compared with a "normal" case. New or neck sized brass may not have shoulders set at exactly the same length. A case with a short shoulder and a long neck may have a smaller volume than a heavier case with a shorter neck. Again, these are small differences, but the various small variations can add up to the difference between first and third place in a match. Most shooters will probably not need to worry about these little details, but those who want to shave 1/8 MOA or so might be interested. __________________ "If the enemy is in range, so are you." - Infantry Journal