not sure why sources make such high mg caps and tablets... the "my dbol is bigger than your dbol" is not really good for the consumer. 5 and 10mg tabs are really ideal, though guess that some will want to take 50mg at once.
the dbol inside the caps could possibly be mixed with whey, in which case you wouldn't be able to split them accurately. ask your source if they are pure or cut before you split them.
You can guarantee that they're cut with a filler otherwise the caps would be stupidly small.
If you have some reasonably fine scales, you could dump out, say 3 caps and then split them into fifths. You might even be able to do it by eye. Be sure to mix thoroughly to help ensure an even distribution. You could even cut them further yourself with glutamine or some other powder to help with evening out the distribution of the dbol and measuring the amounts with decreasing inaccuracay.