Ok, maybe I can work with that, but lets stay away from equations. Your skull scenario is Newtons first Law. But, lets make your brain the bullet in this case. I hope you understand that in this scenario the projectile will stay in motion at a constant velocity until its acted upon. Lets say the primer ignites the powder and the majority of it burns on the way down the tube. So now we're right at the crown or muzzle. Both the gas and bullet are going the same velocity. The bullet is in front of the gas (assuming no gas has blown past or seeped around). Then we hit the atmosphere which acts on the bullet and the gas.

So now we are out of the barrel just a tiny bit. The bullet and the gas are now on a separate journey. The gas wants to expand and it slows down quick and short like a parachute while the bullet continues to haul ass. You talked about the huge flame that came out of your 06. The flame was the expanding gas and unburned powder and your bullet was out in front of that. So a muzzle brake is going to help the gas expand and slow down quicker and in different directions with less opportunity to interfere with the projectile. Does this help?