It's so much easier if you use these capsules and just mash them into the powder (or pour the powder into the lid and then mash the capsule onto it) until packed tight, and then put the small end of the capsule on the other end. You will have a 100mg F-phenibut capsule, pretty reliably/consistently.. Though with something like this, I suggest getting a scale to be sure of accuracy.
Every week I sit with a scale and measure out seven capsules of Bromantane and seven capsules of Tianeptine Sulfate, into tiny little super-swallowable capsules. I measure the caps beforehand (range from 28-30mg each) to be accurate to the milligram.
Capsule filling machines can get messy. I just use this little guy - and it comes with tongs, so I use them to dip the half-capsule in the tub of powder (keeps things sterile). Then I just seal it up with the other half cap, weigh it, and adjust if necessary.
But TBH I'm getting really really good at eyeing 50mg powder. This is not easy at first.