TexasViking
Member
If you said that it ignites the propellant? Winner, winner, chicken dinner as they they say in Lost Wages!
This is a subject, that for many years I have seen speculation on, with many false assumptions concerning Pressure Peak and when it occurs. So for reloaders and ammo enthusiasts here, I will provide some info on this. Some guys that have been handloading as long as I have, or longer, will probably read some things from the “good old days” that I am very appreciative of, and feel like I got started in the “Golden Age” of handloading. And because my personal occupation has required an understanding of pressure in multiple forms, I really miss the days when better information was provided to handloaders, pressure curve analysis in particular. The last such information that I saw came from Western Powder Co. at a time that I believe they had the best ballistican I've ever spoken to. His name was Johan Loubser, who first informed me about the CIP method of pressure testing in Europe around 2001. And in case you're not aware, the 9mm NATO, 5.56mm NATO and the 7.62mm NATO had their Maximum Average Pressures, MAP, estabished via the CIP method. In the interest of avoiding an excessively lengthy first post, I will quote some valuable information that was printed in the Lyman 46th Edition Handloading manual, and it will be printed in italics.
So why does Lyman have higher numbers for their handloading manual editions? Because the very first manual was actually written by the Ideal Reloading Tool Co. in the 1880s and has continued on after the Lyman Gun Sight Co. purchased Ideal in 1925. If you've seen an old western movie where men were sitting around the campfire making handloads, the handtool they are using was likely one of several made by Ideal, whose owner/inventor began after being discharged from the US Army in 1865. Some of these things we can address as the thread progresses. My aim here is to provide those with correct information that they may not have read in their handload manual. And as I've stated before, and what has essentially become an axiom for me: Every Handloader Should Own At least One Lyman Manual! Continuous pressure rated data since before I actually made my first handloaded cartridge in 1986 and manuals going back another hundred years.
The Primer Goes Bang!
"Upon ignition of the propellant by the primer, hot gases begin to build up behind the bullet. During the first fraction of a millisecond, the pressure rise is very gradual. Smokeless propellants, however, burn more rapidly as pressure increases. In other words, the pressure increase causes more rapid propellant burning which in turn causes more gases and higher pressures. This leads to the very rapid pressure increase that starts at about 0.1millisecond.
When the pressure reaches a point (typically less than 10,000 PSI) where the friction force between bullet and case neck is overcome, the bullet begins to move.
Movement of the bullet into the barrel throat increases the expansion volume of the gases. This volume increase tends to lower the pressure. However, the pressure generated before the bullet exits the cartridge causes the powder to burn so fast that gases are generated faster than the volume increases. Chamber pressure therefore continues to rise. The bullet is forced into the rifling and begins to accelerate down the bore.
As the bullet moves down the bore, the expansion volume for the gases increases very rapidly. Chamber pressure then reaches a PEAK VALUE, and then begins to fall."
This is a subject, that for many years I have seen speculation on, with many false assumptions concerning Pressure Peak and when it occurs. So for reloaders and ammo enthusiasts here, I will provide some info on this. Some guys that have been handloading as long as I have, or longer, will probably read some things from the “good old days” that I am very appreciative of, and feel like I got started in the “Golden Age” of handloading. And because my personal occupation has required an understanding of pressure in multiple forms, I really miss the days when better information was provided to handloaders, pressure curve analysis in particular. The last such information that I saw came from Western Powder Co. at a time that I believe they had the best ballistican I've ever spoken to. His name was Johan Loubser, who first informed me about the CIP method of pressure testing in Europe around 2001. And in case you're not aware, the 9mm NATO, 5.56mm NATO and the 7.62mm NATO had their Maximum Average Pressures, MAP, estabished via the CIP method. In the interest of avoiding an excessively lengthy first post, I will quote some valuable information that was printed in the Lyman 46th Edition Handloading manual, and it will be printed in italics.
So why does Lyman have higher numbers for their handloading manual editions? Because the very first manual was actually written by the Ideal Reloading Tool Co. in the 1880s and has continued on after the Lyman Gun Sight Co. purchased Ideal in 1925. If you've seen an old western movie where men were sitting around the campfire making handloads, the handtool they are using was likely one of several made by Ideal, whose owner/inventor began after being discharged from the US Army in 1865. Some of these things we can address as the thread progresses. My aim here is to provide those with correct information that they may not have read in their handload manual. And as I've stated before, and what has essentially become an axiom for me: Every Handloader Should Own At least One Lyman Manual! Continuous pressure rated data since before I actually made my first handloaded cartridge in 1986 and manuals going back another hundred years.
The Primer Goes Bang!
"Upon ignition of the propellant by the primer, hot gases begin to build up behind the bullet. During the first fraction of a millisecond, the pressure rise is very gradual. Smokeless propellants, however, burn more rapidly as pressure increases. In other words, the pressure increase causes more rapid propellant burning which in turn causes more gases and higher pressures. This leads to the very rapid pressure increase that starts at about 0.1millisecond.
When the pressure reaches a point (typically less than 10,000 PSI) where the friction force between bullet and case neck is overcome, the bullet begins to move.
Movement of the bullet into the barrel throat increases the expansion volume of the gases. This volume increase tends to lower the pressure. However, the pressure generated before the bullet exits the cartridge causes the powder to burn so fast that gases are generated faster than the volume increases. Chamber pressure therefore continues to rise. The bullet is forced into the rifling and begins to accelerate down the bore.
As the bullet moves down the bore, the expansion volume for the gases increases very rapidly. Chamber pressure then reaches a PEAK VALUE, and then begins to fall."
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And I have had a few adult beverages tonight 
