Looks about what I get, regarding the amount of fines. I actually screen twice. Once before the grinder, and once after the grinder. I have run my 55 gallon barrel system 275 times, according to my record book, and I have three 6 to 8 foot high compost piles I turn with a front end loader. (I’ll take all the fines I can get, and they get mixed into the compost piles!) My method takes lots of time, too, so I do it every day for a little while. My guess is that smashing the pieces between the bricks is creating more dust and fines. My sifting screen is set up near the path that leads from the house to my workshop, so I can walk past it, screen some, and then go on. I see a few pieces in your “engine ready” charcoal that I would grab and break them into two pieces. They should break easily. If not, then put them in the BBQ charcoal pail. My grinder is the hand operated one, so I save my sorted/screened charcoal for a windy day, put on a dust mask, some heavy gloves, and crank til my arm gives out. Then I screen it again, and go back to the grinder until the arm gets tired. I’ll get enough engine grade charcoal to fill a 55 gallon drum and then I attach the lid and seal it. Later, I open the lid to see if there is any moisture on the bottom of the lid. If so, I wait for a low humidity day, and open the barrel and let it dry out, then seal it back up. Eventually there is no more condensation, and I leave it sealed.
You could mix some of your “BBQ charcoal” in with fuel in a TLUD cooking stove, and now and then toss in a hunk while cooking. My stove makes very good small pieces of excellent charcoal. You might put on some gloves and just break it up with your hands, rather than smashing it with bricks.
After a charcoal grinding session, I notice the water I collect while showering is black!
Oh, I should mention that soft woods like cedar and pine make more dust and fines than hard wood like ironwood, mesquite, huisache or oak. I’m always on the lookout for dead limbs and downed trees for my charcoal making barrel, especially hardwoods.