When I fill my phials I use a Henry Krank small powder flask with a tiny nozzle that has been cut down to size so as to give the right measure. I can roughly adjust the amounts by various means-sticking things in the hole lol. I weigh out the powder on my digital scales for the first few and then line them up and do a visual check. I know that my load is accurate, I have weighed all my phials and they are (surprisingly) more or less identical in weight, consequently loaded phials should all weigh the same. Hence it is easy to check your charge is correct without hassle eg spilling powder.