Thanks for the reply.
I've basically done what you suggest. I pushed a pellet through from the breech. For the first couple of inches the resistance is obvious. Then the pellet becomes loose and the rod/pellet flies down the barrel until you meet the choke at the muzzle end ( last couple of inches ). The resistace returns at that point and remains constant until the pellet exits the barrel. A pellet is really tight if you try and push it in from the muzzle end. So I'm happy that the choke is the tightest area of all. I'm just not happy that the pellet is being sized down at the breech and then loose for the majority of the barrel.
The rodded pellets have land/groove marks equal all round the head and tail with no obvious signs of damage elsewhere.
The crown is fine. It was re machined/finished by John Bowkett when he blueprinted the rifle.