Greetings Louis & Welcome to the Forum! I own and shoot a lot of C&B revolvers, one of them being the 3rd Model Colt Dragoon. I'm using 45 grains of 3Fg Goex, a wonder-wad, and a .454 Hornady ball.
I use a custom built loading stand so as to enable me to pour the powder into the chambers of the cylinder without spilling any. This loading stand also gives me the chance to make sure that I have an equal seating depth of all of the loaded balls. It does take some force to get all of that powder in there with the wad and the ball on top. What I sometimes do to make it a little easier is to first use the ram to push only the powder down further into the cylinder. This leaves plenty of room for the wonder-wad and the ball! I would recommend 40 grains, the wad and a .454 ball for best over-all accuracy, without ramming the powder first. But you did ask for a MAX charge, so I gave it to you!
My Walker will hold 55 grains of powder without the need to use the ram on the powder, but it is most accurate with a 50 grain charge! Accurate enough to win the entire competition at times, even going up against very accurate single-shot pistols with adjustable sights.
The big Dragoons are natural pointers, and I score better with them and the Walker than I do the 1858 Remmy NMA. The rear sight in the notch of the hammer does take some getting used to, but after you learn where to hold it on the target, you will have tight groups! The best advice that I can give you is to pre-measure all of your charges, do EVERYTHING the SAME, and remember not to flinch! Just let the hammer fall on the cap while the gun is still!
One moe thing...most of these horse pistols were sighted-in for 50 or 75 yards, so you have to aim LOW on the target! My Walker is exactly 6.5 inches high at 25 yards. That would be a good place to start for you!
Let us know how you do. We'll be here if you need any more advice.
Dave