Help on powders - Tite Group vs Clays and 9mm vs .45

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Folks,

As I started digging more into powders, I need some help understanding burn rates and application to certain calibers:

1) AA-7 is a relatively slow burning powder and it is perfect for 9mm. .45 ACP being a low pressure case would work better with AA-5 (faster burning than AA-7). I would have thought for the .45 one needs to use slower powder to keep the pressure down and keep that pressure longer to push that heavy bullet out faster but looks to be vise versa - what am I missing here ?

2) On the other hand, Tite Group and Clays have similar burning rates (Clays is a bit slower) but everyone is using Tite Group and does not recommend Clays in 9mm and .40 I do not really understand why Tite Group will be much better for 9mm/.40 than Clays.

Thanks for your help,
Igor.
 
1) in the 45 there is a large area of bullet that the pressure "pushes" against, meaning that you need less pressure for the same force on the bullet.

Pressure acting on a surface, larger surface = greater force

Example:
10,000 psi on 9mm bullet = 990 pounds of force
10,000 psi on 45 bullet = 1,590 pounds of force


2) Clays is much FASTER than Tightgroup. It can be used in 9mm and 40 but only for ligher loads. Stay with published loads.

There are also a powders called INTERNATIONAL Clays and UNIVERSAL Clays which are often confused with Clays. (It was a poor naming choice by Hodgdons). International and Universal are slower than Tightgroup.

Burn Rate Chart here => http://hodgdon.com/burn-rate.html

Some IPSC shooters use Clays for major in 40, BUT the cartridges are loaded longer than spec which reduces pressures. The power charges are well above published loads.
 
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