Low Key, 40 g. should be .40g no matter what measurer your useing, atleast that's my way of thinking. When I place the powder in the cylinder chamber it looks like it has enough room for the ball and that's all. Then I place the wad over the powder and shove it down on the powder with a doll rod so that it's tight and nice an even. Nowit looks like I can only get a half a ball on top of that but you can load a ball over the wad with ease. You need to apply presure with the ram and seat it untel it will not go any more. That should leave you some space on top of the ball as you see in the picture.
When you place the powder in your cylinder just lightly tap the side of the chamber to settle the powder a little if you want. There is no reason for 40g to fit in one chamber but not in another . I have two cylinders for each of my .44 Remingtons and they all hold the same amount of powder.
If I were to leave out the wad I could get 45g in the Remington but I see no need to go that high. It may be that your not compressing the ball down as hard as you should. The rams can take much more preasure than you think.Just give it a try and see how it goes. Make sure you are measuring out 40 g before doing anything.