big al hunter
New member
A couple of recent threads have left me wondering enough that I went back to review some research I did some time ago. I spent a fair amount of time researching the pressure ratings of .223 and 5.56. It makes no sense to me that very near to exactly the same cartridges would have a 7,000 psi difference in pressure. My studies left me thinking that an awfully large percentage of the gun world is confused.
One of the articles I read that sparked my search for more knowledge was from a gun magazine. I can't remember now which one. The author was curious about the pressure difference between 223 and 5.56. He put pressure reading equipment on production rifles with both chambers and fired both loads in all of the rifles. Some of the 223 loads had higher pressure than 5.56 in the same chamber. That got me thinking. Why....
My research found that the military has 2 different specifications for 5.56, that have different pressure limits. The limit many people quote for 5.56 is 62,000 psi. This appears to be due to the NATO EPVAT specification for pressure of 62,366 psi (430 mpa). The second specification is US military SCATP with a max pressure of 55,114 psi (380 mpa). Which is the commonly used pressure for .223.
When I found these specifications it made me even more curious. I used some Google Fu and found that the 2 systems are used because in the US ammunition is produced using SAAMI specified testing method. Which happens to match SCATP specifications. Foreign military ammunition manufacturers do not use SAAMI specified pressure testing. NATO created the EPVAT specification for their use. The 2 specifications test the pressure at different locations with different protocols. Thereby giving us 2 different pressure numbers for the same cartridge/load.
I know there is a difference in the 5.56 chamber that allows use of heavy for caliber bullets. And that using 5.56 ammo in .223 chambers could cause issues with pressure. Possibly making it dangerous. But the standard test pressure is the same for .223 and 5.56 when using the same measurement specification.
My questions:
1. Why is this not common knowledge?
2. Do your loading manuals show pressure for loads tested as 5.56?
Of the 3 loading manuals I have, none show a pressure for 5.56. Hornady 9th edition has 3 sections, 2 for 223 and one for 5.56. But no pressure is listed. Nosler Reloading Guide 8 shows both cartridges, but no pressure. Lyman 49th shows pressure in CUP (different discussion) but no section on 5.56.
One of the articles I read that sparked my search for more knowledge was from a gun magazine. I can't remember now which one. The author was curious about the pressure difference between 223 and 5.56. He put pressure reading equipment on production rifles with both chambers and fired both loads in all of the rifles. Some of the 223 loads had higher pressure than 5.56 in the same chamber. That got me thinking. Why....
My research found that the military has 2 different specifications for 5.56, that have different pressure limits. The limit many people quote for 5.56 is 62,000 psi. This appears to be due to the NATO EPVAT specification for pressure of 62,366 psi (430 mpa). The second specification is US military SCATP with a max pressure of 55,114 psi (380 mpa). Which is the commonly used pressure for .223.
When I found these specifications it made me even more curious. I used some Google Fu and found that the 2 systems are used because in the US ammunition is produced using SAAMI specified testing method. Which happens to match SCATP specifications. Foreign military ammunition manufacturers do not use SAAMI specified pressure testing. NATO created the EPVAT specification for their use. The 2 specifications test the pressure at different locations with different protocols. Thereby giving us 2 different pressure numbers for the same cartridge/load.
I know there is a difference in the 5.56 chamber that allows use of heavy for caliber bullets. And that using 5.56 ammo in .223 chambers could cause issues with pressure. Possibly making it dangerous. But the standard test pressure is the same for .223 and 5.56 when using the same measurement specification.
My questions:
1. Why is this not common knowledge?
2. Do your loading manuals show pressure for loads tested as 5.56?
Of the 3 loading manuals I have, none show a pressure for 5.56. Hornady 9th edition has 3 sections, 2 for 223 and one for 5.56. But no pressure is listed. Nosler Reloading Guide 8 shows both cartridges, but no pressure. Lyman 49th shows pressure in CUP (different discussion) but no section on 5.56.