Quote Originally Posted by bigjeepman View Post
Could you give an example or a source for this? I cannot imagine that being the case but it could very well be.

I found quite a few places on the web that talk about reduced velocity when switching to a magnum primer for the same load. Reduced velocity almost always means reduced pressure, all other things being exactly the same. I remember reading at least one article that had some pressure testing with it, but I don't remember the search terms I used or where it was. One theory, not proven is that the extra push from a magnum primer causes the bullet to "jump" into the throat before the powder gets burning, thereby increasing the volume and reducing the pressure. Sounds a bit off but perhaps it is true. Multiple individuals have experienced reduced pressure signs and reduced velocity when substituting a magnum primer for a standard, so I pretty much bought into it until I see something different. That doesn't mean you can't get an increase in pressure, but that is not always the case.

https://www.google.com/search?client...+magnum+primer