There is no predictable percentage. Too many variables. I have seen data where substituting magnum primers caused a big increase in pressure, and, less often, where it made little or no difference.
I have also seen data where it reduced velocity variation and improved accuracy, but more often the reverse.
Substitution will probably make less difference in the .45 than in a higher pressure cartridge, but you will have to work up the load to find out for sure.
I have also seen data where it reduced velocity variation and improved accuracy, but more often the reverse.
Substitution will probably make less difference in the .45 than in a higher pressure cartridge, but you will have to work up the load to find out for sure.
