I'm with you on the bullet weight 3DogMike, biggest I have seen referenced in the various .500 BPE's is 440Grains. The577/500 Magnum was regulated for the 440 as was my 577/500 No 2. The 650 Grain bullets were in .577 calibers, 750 in the "full" 577 Nitro load with a 650Gr in the 577 Nitro "Light". Not sure what lead bullets were loaded in the 577BPE's.