I chrono'd some homeloads today and found them about 300ft/sec off the quoted values in the manual. I'm not hung up on velocity and know I wouldn't get book values. My loads are accurate and that will do for me, I'm not chasing speed, just curious to understand the science behind it.
My load is 25grn of Benchmark under a .224 55grn Nosler BT.
I know my rifle is nowhere near the same as the one used in the Nosler manual, there's is 24" 1in12 twist mine is a 20" 1in9. I'm wondering which bit is effecting my speed, barrel length or twist, or probably a combination of both.