Why more powder for 223 than 556

[T2C]

There is a water capacity chart floating around somewhere where about ten or so different cases were tested / compared. Will try to dig it up and post it...

ETA:

http://i2.photobucket.com/albums/y17...iesresized.jpg

I used Isopropyl alcohol to measure case volume to develop .30 caliber 1,000 yard loads. Loss of liquid when dumping into and back out of the case made it less accurate than I anticipated. I weighed cases, both .223 and .308 cases, to sort them and found that sometimes a case with thinner brass thickness at the case mouth weighed more than a case with thicker brass at the case mouth due to differences in head thickness, web thickness and other factors.

[mRad]

Case capacity also varies pretty drastically year to year, lot to lot. I seem to recall back in the mid-2000s a guy on a precision shooting forum measuring differences in LC stamp and seeing a .2 gr capacity difference from one year to the next. That’s over 5%.


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[DG23]

I used Isopropyl alcohol to measure case volume to develop .30 caliber 1,000 yard loads. Loss of liquid when dumping into and back out of the case made it less accurate than I anticipated. I weighed cases, both .223 and .308 cases, to sort them and found that sometimes a case with thinner brass thickness at the case mouth weighed more than a case with thicker brass at the case mouth due to differences in head thickness, web thickness and other factors.

Much wisdom there.

Anyone who has ever wet tumbled will know that 'it takes a bit to get all of the water out of the case'. You are not just going to turn it over and the case be completely empty and dry.

[T2C]

Much wisdom there.

Anyone who has ever wet tumbled will know that 'it takes a bit to get all of the water out of the case'. You are not just going to turn it over and the case be completely empty and dry.

That's what I found out. I also tried measuring case weight, then adding liquid while the case was on the scale. Problem was that I could not see air bubbles inside the spent primer and primer pocket. Isopropyl alcohol was more consistent than tap water or distilled water, but you still had to wait a considerable amount of time to see if you had to add any liquid to the case. If you tried to measure the liquid by volume as it went into the case, it was difficult to do it consistently enough to reduce error.

I marked twenty cases and tried to measure case volume twice a day, five days in a row. I left the electronic scale on the entire week, so there would not be issues with warm up error. Out of ten readings for each cartridge case, I saw three to four different values for each case.

I gave up on measuring case volume, because I was not seeing higher scores at 1,000 yards. I focused on sorting cases by headstamp, case wall thickness, trim length and number of times fired.

Back to the original concern by the OP. Hornady has chamber pressure and temperature measuring equipment most people do not. A lot of testing goes into their research before they publish reload data and comments for each cartridge. I base my reloading on what Hornady suggests and group sizes. If they say there is a difference between 5.56mm and .223 Rem. chamber pressures, I'll take their word for it.

[mRad]

Having a load that is well into the node will help much more than minor changes in case volume within the same stamp.


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[triggerjerk]

I'll be posing the question to the powder manufacturers later today after a couple more football games have been played. With luck, we'll have their feedback sometime next week....

[s4s4u]

No they aren't. Most mil brass and commercial weigh the same. (7.62 is a different story.)

Oh there are differences in case thickness in 5.56/.223 all right. My pet load that will fill a Remington .223 case up to the neck was nearly overflowing one 5.56 case, IIRC PPU, and varying levels in other brands. None exactly the same, although all cases within a brand seem consistent.

[ViniVidivici]

Having a load that is well into the node will help much more than minor changes in case volume within the same stamp.


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This.

For my match-grade stuff, I do sort by headstamp, but no damn way am I weighing cases. My best loads are sub-MOA.

Sometimes perfection can be the enemy of good.

[HKGuns]

The Hornady 9th and 11th editions have similar data sets as the data sets you are using, the 8th doesn't have 556 listed. I looked at XBR for 55 grain bullets.

[T2C]

Having a load that is well into the node will help much more than minor changes in case volume within the same stamp.


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Center of accuracy node is what I shoot for and it does not always coincide with low Extreme Spread and Standard Deviation numbers.