I know slow powders need to concern about flashover and loaded to high fill rate or use filler when loaded low. Hodgdon has 7.62x39 load data for Banes 108gr RRLP with IMR 4227 and it shows starting load only 15.0 gr and max 17.6 gr. 15 gr is only a bit over 50% fill and 4227 is a medium burn rate powder. I load 123 gr cast bullet with 16 gr 4227 based on the data but I have to wonder if I should use filler to be safe! So how low a burn rate needs to worry about flashover! It is Hodgdon data, it must be safe! Banes load data shows 18.6 - 20.6 gr 4227 for the bullet.