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308 over pressure?
- Thread starter Holeshot
- Start date
Sorry, let me elaborate. The only brass that I have ever had a split case neck is federal and it was on the first reload. The brass is soft it work hardens easily and in my house it goes in the garbage can. I have never had anything but bad luck with winchester primers they are always smaller than federal making for loose pockets and I had a batch of them blow out the side with a very light load leaving pitting in the bolt face of a near new rifle. I currently only use lapua brass and federal primers its not worth messing up a high dollar rifle or my eyes.
josh.rizzo
You are 100% correct, Quickload data is noting more than "ball park" information. The Quickload charts I posted were for comparison of case capacities only, in order for Quickload to give more accurate data you need a chronograph. You then change the burn rate in Quickload until your chronograph velocities match Quickload velocities. Bottom line Quickload doesn't give accurate information until you calibrate it to "YOUR" firearm.
When you see a pressure test barrel and universal receiver used for the pressure and velocity data the chamber and bore are minimum SAAMI dimensions to give the highest possible pressures. You see this in the Lyman manual and in other manuals a specific firearm is used and the data was gathered with a strain gauge glued to the barrel and calibrated with a known pressure cartridge. Meaning a smaller diameter chamber and bore will generate higher pressures and a fat sloppy military chamber will generate lower pressures.
Below is an example of strain gauge being used and calibrated with a cartridge of a known chamber pressure. This chart is from a .223/5.56 pressure testing differences from the the luckygunner.com. Look at the far left green bar showing approximately 49,000 psi and now look at the far right blue bar at approximately 55,000 psi.
What this shows is factory loaded .223 ammunition is loaded approximately 6,000 psi below the maximum rated chamber pressure of 55,000 psi.(liability buffer) It also shows that military ammunition is loaded much closer to the maximum rated pressure of 55,000 psi.
Another important thing to remember is all three pressures listed below are the same exact pressure measured three different ways. The pressures listed below are the normal max rated pressures for "BOTH" the .223 and 5.56 cartridge.
1. 52,000 cup SAAMI copper crusher method
2. 55,000 psi SAAMI transducer method
3. 62,000 psi European CIP method with the transducer located at the case mouth.
The SAAMI measures pressure at the midpoint of the case and this mixed data causes confusion between the .308/7.62 and the .223/5.56.
It is also important to know that brass hardness can vary and measuring base expansion is just another "ball park" indication of excess pressure. I have a bucket full of factory loaded Federal brass that have oversized primer pockets after the first firing, meaning the brass was very soft. This is why testing brass from one batch/lot without pressure and hardness data of the brass is worthless.
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josh.rizzo
You are 100% correct, Quickload data is noting more than "ball park" information. The Quickload charts I posted were for comparison of case capacities only, in order for Quickload to give more accurate data you need a chronograph. You then change the burn rate in Quickload until your chronograph velocities match Quickload velocities. Bottom line Quickload doesn't give accurate information until you calibrate it to "YOUR" firearm.
When you see a pressure test barrel and universal receiver used for the pressure and velocity data the chamber and bore are minimum SAAMI dimensions to give the highest possible pressures. You see this in the Lyman manual and in other manuals a specific firearm is used and the data was gathered with a strain gauge glued to the barrel and calibrated with a known pressure cartridge. Meaning a smaller diameter chamber and bore will generate higher pressures and a fat sloppy military chamber will generate lower pressures.
Below is an example of strain gauge being used and calibrated with a cartridge of a known chamber pressure. This chart is from a .223/5.56 pressure testing differences from the the luckygunner.com. Look at the far left green bar showing approximately 49,000 psi and now look at the far right blue bar at approximately 55,000 psi.
What this shows is factory loaded .223 ammunition is loaded approximately 6,000 psi below the maximum rated chamber pressure of 55,000 psi.(liability buffer) It also shows that military ammunition is loaded much closer to the maximum rated pressure of 55,000 psi.
Another important thing to remember is all three pressures listed below are the same exact pressure measured three different ways. The pressures listed below are the normal max rated pressures for "BOTH" the .223 and 5.56 cartridge.
1. 52,000 cup SAAMI copper crusher method
2. 55,000 psi SAAMI transducer method
3. 62,000 psi European CIP method with the transducer located at the case mouth.
The SAAMI measures pressure at the midpoint of the case and this mixed data causes confusion between the .308/7.62 and the .223/5.56.
It is also important to know that brass hardness can vary and measuring base expansion is just another "ball park" indication of excess pressure. I have a bucket full of factory loaded Federal brass that have oversized primer pockets after the first firing, meaning the brass was very soft. This is why testing brass from one batch/lot without pressure and hardness data of the brass is worthless.
This is all very interesting information. Thanks! I am learning a lot.
