If you have a standard King Arms type, 200 round Speedloader, then one full press gives you 4 BBs, but the 1st BB you load and the last one, are effectively lost because of how the Speedloader works.
So 9 full presses of 4, minus the 2 you lose from the Speedloader's mech, and the 4 you drop when you reload, gives you exactly 30 usable shots.
Just make sure you buy a transparent Speedloader lol.