Re: 450 3 1/4 nitro
Are you shooting an older double rifle? I have done a lot of work with a Holland and Holland-450 Nitro Express that is 3 1/4" long. It is based in the same case as a 500 Nitro but necked down to 450. If your cartridge is the narrower Rigby 450 Nitro, my load will be too HOT. In order to meet original velocity specs and impact points I used 74 grains of IMR3031, 2 grains of Kapoc filler, Federal magnum primers. These roundjs were originally loaded with Cordite, you cant fill the whole case with modern powders so you will need the filler to take up space and keep you powder against the primer. Most importantly had to use either original Kynock 480gr bullets or currently manufactured 480 grain Woodleigh bullets. This was needed to regulate the impact points of the double barrels. The original ogive is critical in a douce for regulation of the two barrels. If your shooting a single barrel you may be ok with modern bullet designs. They didn't shoot well in my rifle, even out of one barrel. This load exactly duplicates the original velocity of 2150fps band the pressure is mild. The accuracy spec from H&H on my double wa 2 shots from each barrel into 1.5" a 50 yards. Used this rifle and load about 20 years ago to shoot a lion in Botswanna. Hope this helps.