Broken S.
I know that the faster powder reaches the peak cup quicker. Is this why?
Yes. CUP is a system to measure pressure in a chamber. and it is confusing when both PSI and CUP are used in the same loading book.
It is assumed that either is measured in the center of a case but that not always done, This is one reason why pressure readings from different sources vary a great deal. Some German sources measure pressure in the neck. Of course a strain gage can be attached anywhere.
This is why we need to start with a lesser powder charge like Mac says 5-10% of what the book says. Otherwise you may compare apples with oranges.
In the 25-06 I consider a max load about 60kpsi in a good bolt action that is ok. But individual loads and guns can easily vary 10%.
So when I recommend a 51kpsi you are 15% below max in a 25-06. now when you consider a plus or minus 10% in that loading you can easy reach 56Kpsii with that load. So a 15% margin is not being too conservative.
Also remember values in loading books are also averages. So when loading a Handi I like to maintain that safety factor. Not just for the reason of safety but for accuracy that comes from lower vibration and the lesser strain/uplift on the latch.
The reason I recommend a slow burning powder for the Handi is besause it has longer and and lower pressure spike. Which means lower chamber pressure but overall longer pressure duration. The later will give you increased velocity with overall lower pressure, while a faster burning powder does most of it in the chamber. Not very benficial in a Handi.
A slower buring powder also has abetter case fill ratio, which will give you more uniform ignitition. We been through all this before and the concept is very basic. Hope this makes some sense.
