I am reloading for 9mm with AA#5 and have some new Rainier 147 grain TRN bullets. I see in several different manuals as much as 0.8 to 1.0 grain of powder difference for FMJ vs plated bullets. When we are talking about the same weight bullet and extremely similar shape, what is the big difference between FMJ, plated or jacketed RN?? Aren't the plating and jackets all copper? Why would there be so much difference to get the same FPS also? Any thoughts out there on this?
Thanks
Thanks