pressure limits?

[sanjuro893]

I was looking at the manual for my 9mm and one page has a warning about pressure limits. For 9mm it says the limits are 124 gr. and 1225 ft. per sec. So is that telling me I shouldn't go with a heavier bullet weight or lighter?

 

[grwd]

You're reading it wrong, speed is a result of pressure, not a variable for it. bullet weight is bit one variable concerning pressure.
Read up more on some online reloading manuals

 

[sanjuro893]

You're reading it wrong, speed is a result of pressure, not a variable for it. bullet weight is bit one variable concerning pressure.
Read up more on some online reloading manuals

Okay. Thanks for the info!

 

[Blitzfike]

The science of internal ballistics is a very complex subject. Basically, smokeless powder doesn't normally explode like black powder, it "deflagrates", meaning that it burns at varying rates depending on the size of the cartridge, the bore diameter, the weight and makeup of the projectile, the primer, and the amount of crimp to list the most common components of the process. There is much more to it, as to the burning rate of the powder which may be varied by the size and shape of the grains, what they are coated with and whether it is a single base powder (nitrocellulose) or a double base powder. (nitro cell. and nitro gl.) The depth to which you seat the bullet has an effect on the pressure as it changes the inner case capacity in which the powder burns. That is why it is dangerous to seat bullets deeper than the load calls for with certain powders. I load a lot of Accurate #5 in 40SW. I have to be careful when clearing the weapon that when I re-chamber a round, I don't cause the bullet to be seated deeper from repeated chambering. If that happens, the pressures in that particular case powder bullet combination can generate dangerous pressures. You can vary the powder for lighter or heavier bullets to keep pressures within the specified limits. Follow the loading guides and you won't have much problems. Good luck with the hobby. Blitzfike

 

[Hobbes]

I was looking at the manual for my 9mm and one page has a warning about pressure limits. For 9mm it says the limits are 124 gr. and 1225 ft. per sec. So is that telling me I shouldn't go with a heavier bullet weight or lighter?

Given the same propellant charge, a lighter bullet will generate less chamber pressure than a heavier bullet.

Study the reloading manuals for a given caliber-propellant but different bullet weights.
You will notice that as the bullet weight increases, the propellant charge is decreased.

Modern propellants are progressive; they burn faster when they are under more pressure.
So, with a heavier bullet to push they are under more pressure and burn progressively faster.
Therefore, the charge must be reduced for the heavier bullet to maintain the same pressure.