I'm shooting Book load max charges ( Flattened primers) 75gr ELD in front of 25grs of Re#15.5 and I bolt locks open on very last shot When burning Alliant Power Pro 2000-MR (Again book max charges) 28.2 grs behind an 80.5 Berger full bore bullet the bolt doesn't lock open, Why? I'm pushing those bullets above 2900FPS and MOA accuracy. Again, why?