Just got a Parker-Hale .451 Volunteer rifle,beautiful rifle......I bought 40 bullets from Track of the Wolf but they are a very tight fit. I have a .449 push through sizer, and a .450 sizer on the way. I also have a source for .445 300 gr hollow base bullets. Some people say not to use undersize bullets in the .451 rifles because it might "shift forward", yet .575 Minies have been used in .58 bores since forever ago, I've fired thousands of .575 Minies in .58 rifles, and .533 Minies in my .54 Mississippi.....I can't see why a .445 in a .451 would be different. I'm going to just try different bullets and see what works, it's part of the fun.