Brass weight discrepancies

gyrfalcon

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I noticed that Nosler .270 Win brass unfortunately comes in two weights.
178 grains/case and 201 grains per case. Making a 23 grains weight difference per case.
201 grains is 12.9% heavier then 178 grains.
My favourite 270 Win load with 178 grain brass is already a safe hot one in my rifle.
Would you guys agree that I should drop my powder charge 12.9%, when I switch from 178 grains brass to 201 grains brass? Or is this a wrong assumption on my side?
Yes, I realize I can start ladder testing all over again, but try to save time, effort and money for this fine Cooper hunting rifle.
 

MagnumManiac

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No, dropping a powder that much can be dangerous.
Just work back up from 5% below max, there will be another node in that range of testing.
If you measure the capacity difference in grains of water, you may find that the capacity isn’t really that much different.
Nosler brass was made by 3 companies now. The very early stuff was Federal, then Norma and now whoever is making it, the rumours say it is in house, but I don’t know that 100%.

Cheers.
 

Coyote Shadow Tracker

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Couldn't you just fill one case with the powder in question and try to fit it in the other? Then reverse? That would give you real world capacity for the powder and weight the difference and do some math...

I know water could be used but who shoots water guns anymore?
Liberals-maybe?
 

QuietTexan

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Water has a higher surface tension than isopropanol, so water will form a larger meniscus on the mouth of a case. Isopropanol is hydrophillic and miscible with water, and using the mixture will result in a more accurate volumetric measurement due to reduced variability on the amount that protrudes above the case.

Big words for "more accurate" :D
 

gyrfalcon

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Water has a higher surface tension than isopropanol, so water will form a larger meniscus on the mouth of a case. Isopropanol is hydrophillic and miscible with water, and using the mixture will result in a more accurate volumetric measurement due to reduced variability on the amount that protrudes above the case.

Big words for "more accurate" :D
Thank you for the information 👍👍
 

entoptics

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Assuming the volume difference is entirely represented by the weight difference (not likely the case), brass is ~8X as dense as H2O or powder. So you're 23 grain difference in brass weight would only be 3-4 grains of powder capacity. The nominal 270 powder capacity it 67 grains H2O. So that's an ~5% difference in capacity.

Thing is velocity (pressure) does not linearly change with capacity. On top of that, it will vary based on the burn rate of the powder used. It all relates to expansion volume. On a basic level, it's why you can get higher velocity out of a magnum cartridge at the same pressure, but to do that, you need to add more powder...

Anyway, I did some experiments awhile back. Though not nearly as extreme a difference as your situation, they may be helpful...


I did some other less rigorous testing on variable head stamped brass (308 and 556), and if I remember right, I was seeing a range of 1-4 fps per grain of brass weight. Take the middle of that, and you're looking at 40-50 fps for your situation. That's probably about 1 grain of powder in a 270 win.

If I were in your situation, I'd take the heavy brass and I'd load up 2 rounds each at -2, -1.5, and -1 grains and shoot them over a chrony. I'd bet you'll be near the light brass with 1-1.5 grains less powder in the heavy brass.
 

Philward

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I noticed the same weight difference with nosler brass in the 30 nosler. 3 different headstamps, one set of 18 cases being lighter by about 20grains. These may have been the factory rounds that were shot initially.
 

skipglo

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I noticed that Nosler .270 Win brass unfortunately comes in two weights.
178 grains/case and 201 grains per case. Making a 23 grains weight difference per case.
201 grains is 12.9% heavier then 178 grains.
My favourite 270 Win load with 178 grain brass is already a safe hot one in my rifle.
Would you guys agree that I should drop my powder charge 12.9%, when I switch from 178 grains brass to 201 grains brass? Or is this a wrong assumption on my side?
Yes, I realize I can start ladder testing all over again, but try to save time, effort and money for this fine Cooper hunting rifle.
Check internal volume of both, weight is not a factor if internal volume is a constant.
 

gyrfalcon

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Oct 13, 2021
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Location
calgary, Alberta
Assuming the volume difference is entirely represented by the weight difference (not likely the case), brass is ~8X as dense as H2O or powder. So you're 23 grain difference in brass weight would only be 3-4 grains of powder capacity. The nominal 270 powder capacity it 67 grains H2O. So that's an ~5% difference in capacity.

Thing is velocity (pressure) does not linearly change with capacity. On top of that, it will vary based on the burn rate of the powder used. It all relates to expansion volume. On a basic level, it's why you can get higher velocity out of a magnum cartridge at the same pressure, but to do that, you need to add more powder...

Anyway, I did some experiments awhile back. Though not nearly as extreme a difference as your situation, they may be helpful...


I did some other less rigorous testing on variable head stamped brass (308 and 556), and if I remember right, I was seeing a range of 1-4 fps per grain of brass weight. Take the middle of that, and you're looking at 40-50 fps for your situation. That's probably about 1 grain of powder in a 270 win.

If I were in your situation, I'd take the heavy brass and I'd load up 2 rounds each at -2, -1.5, and -1 grains and shoot them over a chrony. I'd bet you'll be near the light brass with 1-1.5 grains less powder in the heavy brass.
Thank you for your detailed research. I will follow your recommendation
 
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