10% difference in case weights!

flintlock.50 · October 13, 2010, 08:33 PM

I've been working with a box of Nosler .30-06 cases. I didn't pay too much attention to the notation on the box that the cases were "weight sorted." I thought that would be important mostly to bench rest shooters.

Tonight, while loading, I noticed that the powder charge in one case was considerably higher (in the neck) than in some others. I double checked the charge weights and they were right on. So I weighed quite a few empty cases. I found that one group was 20 grains lighter than the other! That's basically a 10% difference! The "light" cases all weigh the same and the "heavy" cases all weigh the same. But there's that pesky 20 grain difference.

Since the heavy cases have less capacity, I presume they will generate higher pressures. I'll chronograph the velocities of the light and heavy cases, but I'm very surprised to find so much difference in Nosler cases.

Is this typical? Should I be concerned about segregating the cases? Any experience in how much this might affect pressures and velocities?

Thanks,

flintlock.50

mehavey · October 13, 2010, 09:15 PM

Something is seriously wrong.

Loading them the same would result in conditions not unlike a 30-06 charge in a 308 case. (Well... sorta. a 20gr difference in brass is ~ 2-1/2gr difference in case water volume. That would turn a nominal 56,000psi chamber pressure into 61,000psi -- 1,000psi over Max)

I just weighed 15 new/unfired WW 30-06 cases and got the following:

Average: 187.1
Median: 187.1
Low: 185.5
High: 188.7
Extreme Spread: 3.2
Std Dev: 1.1 (Means 95% of all cases would be +/- 2.2gr)

I'd slice a "heavy" and "light" case lengthwise with a Dremel and take a look at the internal profiles.

Brian Pfleuger · October 13, 2010, 09:58 PM

That's a pretty incredible difference. I just weighed a batch of Norma 7mm-08 cases from two different lot numbers. The lightest was 165.6gr and the heaviest 167.0gr. There were two at 167, all others were within .5gr of 166.0, with the majority being 166.3.

F. Guffey · October 13, 2010, 10:44 PM

I match head stamps, on military cases I match codes and dates, 26 grains is what I would expect. AND no one weighs a case before the first firing and compares the weight of the original weight after firing and trimming. Again, at the Dallas Market Hall Gun Show a shooter/reloader was complaining about head space, we measured the only case he had? , the wall case body measured .002 thousands. We never thought of weighing the case but for the weight to be a value, we would have had to know how much the case weighed when it was new, before it had been fired 40 + times, and yes as the case got lighter,the volume increased.

I loaded 200 rounds of 30/06 on the Dillon 550B, I weighed all the components, the cases were Federal, R-P, military LC and Winchester , WW and WRA, straight across, the military cases were the heaviest and anything Winchesters was 23 to 27 grains lighter, for me it would be disturbing to not know the weight of the components and after loading 200 rounds find a 27 grain spread.

A light weight case has more volume, a heavier case has less volume, then the military case has a thick web and thin body meaning the column of powder in the military case is longer because of the thin case head and a column that is smaller in diameter because the case body is thicker (than a commercial case) so yes, if cases have different head stamps expect the height of the powder in the case to be different.

F. Guffey

F. Guffey · October 13, 2010, 11:00 PM

"thin web (.200 + very little) and a thick body"

R-P cases in 30/06 have a case head thickness of .260+ with a thin case body.

and yes I know the top of the web is concaved, not being flat makes it difficult to impossible to measure for some.

Sorry about that,

F. Guffey

flintlock.50 · October 14, 2010, 08:11 AM

I wasn't very clear in my first post. This weight difference is between two different boxes of Nosler cases. I mixed the lots, never dreaming there would be this much difference. The difference in powder level caught my attention so I weighed some cases and found the weight difference.

One lot of cases has been fired 2-3 times; the other batch has been fired only once. None of the cases have been trimmed yet. I don't know whether the newer or older cases are the light or heavy ones.

My case weights include a primer, but I got 206 grains and 186 grains for the two lots. Weights within a given lot were very close (within a few tenths of a grain).

Visually, the difference in powder level between the two lots is about 1/10 inch. That's an eyeball number, not a measured number.

flintlock.50 · October 16, 2010, 01:43 PM

I chronographed lots of shots today and found that the 10% difference in case weight does matter.

Load data:
.30-06
165 grain Hornady SST Interlock
3.222" OACL
IMR 4350

At both 57.0 and 57.5 grains the heavier cases averaged 37 fps faster than the light weight cases. At 58.0 grains, the heavier cases averaged 92 fps faster than the lighter cases! WOW! There were no signs of high pressure on any of the loads.

I checked just a few 150 grain SSTs loaded 1.0 grain below maximum and the heavier cases also produced 37 fps more velocity, the same as the 165 grain loads.

It looks like I'll have to segregate my cases and adjust loads for the lighter weight cases.

October 13, 2010, 08:33 PM	#1
flintlock.50 Senior Member Join Date: July 1, 2009 Posts: 233	10% difference in case weights! I've been working with a box of Nosler .30-06 cases. I didn't pay too much attention to the notation on the box that the cases were "weight sorted." I thought that would be important mostly to bench rest shooters. Tonight, while loading, I noticed that the powder charge in one case was considerably higher (in the neck) than in some others. I double checked the charge weights and they were right on. So I weighed quite a few empty cases. I found that one group was 20 grains lighter than the other! That's basically a 10% difference! The "light" cases all weigh the same and the "heavy" cases all weigh the same. But there's that pesky 20 grain difference. Since the heavy cases have less capacity, I presume they will generate higher pressures. I'll chronograph the velocities of the light and heavy cases, but I'm very surprised to find so much difference in Nosler cases. Is this typical? Should I be concerned about segregating the cases? Any experience in how much this might affect pressures and velocities? Thanks, flintlock.50

October 13, 2010, 09:15 PM	#2
mehavey Senior Member Join Date: June 17, 2010 Location: Virginia Posts: 6,940	Something is seriously wrong. Loading them the same would result in conditions not unlike a 30-06 charge in a 308 case. (Well... sorta. a 20gr difference in brass is ~ 2-1/2gr difference in case water volume. That would turn a nominal 56,000psi chamber pressure into 61,000psi -- 1,000psi over Max) I just weighed 15 new/unfired WW 30-06 cases and got the following: Average: 187.1 Median: 187.1 Low: 185.5 High: 188.7 Extreme Spread: 3.2 Std Dev: 1.1 (Means 95% of all cases would be +/- 2.2gr) I'd slice a "heavy" and "light" case lengthwise with a Dremel and take a look at the internal profiles. Last edited by mehavey; October 13, 2010 at 09:42 PM.

October 13, 2010, 09:58 PM	#3
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	That's a pretty incredible difference. I just weighed a batch of Norma 7mm-08 cases from two different lot numbers. The lightest was 165.6gr and the heaviest 167.0gr. There were two at 167, all others were within .5gr of 166.0, with the majority being 166.3. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

October 14, 2010, 08:11 AM	#6
flintlock.50 Senior Member Join Date: July 1, 2009 Posts: 233	I wasn't very clear in my first post. This weight difference is between two different boxes of Nosler cases. I mixed the lots, never dreaming there would be this much difference. The difference in powder level caught my attention so I weighed some cases and found the weight difference. One lot of cases has been fired 2-3 times; the other batch has been fired only once. None of the cases have been trimmed yet. I don't know whether the newer or older cases are the light or heavy ones. My case weights include a primer, but I got 206 grains and 186 grains for the two lots. Weights within a given lot were very close (within a few tenths of a grain). Visually, the difference in powder level between the two lots is about 1/10 inch. That's an eyeball number, not a measured number. Last edited by flintlock.50; October 14, 2010 at 08:18 AM.

October 16, 2010, 01:43 PM	#7
flintlock.50 Senior Member Join Date: July 1, 2009 Posts: 233	The data is in! Case weight matters! I chronographed lots of shots today and found that the 10% difference in case weight does matter. Load data: .30-06 165 grain Hornady SST Interlock 3.222" OACL IMR 4350 At both 57.0 and 57.5 grains the heavier cases averaged 37 fps faster than the light weight cases. At 58.0 grains, the heavier cases averaged 92 fps faster than the lighter cases! WOW! There were no signs of high pressure on any of the loads. I checked just a few 150 grain SSTs loaded 1.0 grain below maximum and the heavier cases also produced 37 fps more velocity, the same as the 165 grain loads. It looks like I'll have to segregate my cases and adjust loads for the lighter weight cases.

October 13, 2010, 10:44 PM	#4
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	I match head stamps, on military cases I match codes and dates, 26 grains is what I would expect. AND no one weighs a case before the first firing and compares the weight of the original weight after firing and trimming. Again, at the Dallas Market Hall Gun Show a shooter/reloader was complaining about head space, we measured the only case he had? , the wall case body measured .002 thousands. We never thought of weighing the case but for the weight to be a value, we would have had to know how much the case weighed when it was new, before it had been fired 40 + times, and yes as the case got lighter,the volume increased. I loaded 200 rounds of 30/06 on the Dillon 550B, I weighed all the components, the cases were Federal, R-P, military LC and Winchester , WW and WRA, straight across, the military cases were the heaviest and anything Winchesters was 23 to 27 grains lighter, for me it would be disturbing to not know the weight of the components and after loading 200 rounds find a 27 grain spread. A light weight case has more volume, a heavier case has less volume, then the military case has a thick web and thin body meaning the column of powder in the military case is longer because of the thin case head and a column that is smaller in diameter because the case body is thicker (than a commercial case) so yes, if cases have different head stamps expect the height of the powder in the case to be different. F. Guffey

October 13, 2010, 11:00 PM	#5
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	"thin web (.200 + very little) and a thick body" R-P cases in 30/06 have a case head thickness of .260+ with a thin case body. and yes I know the top of the web is concaved, not being flat makes it difficult to impossible to measure for some. Sorry about that, F. Guffey