The twist lock barrels will be more gentle on smaller bore paint. This is because the barrel back is the same size as the control bore. The next ball in the stack is still sitting above the contact point of the bolt. In a ULE body, the breach is full size and the next ball in the stack actually sits down in the breach area allowing it to get clipped by the tip of the bolt as it fires. This is more pronounced when using small bore paint, because it allows the next ball to sit farther down in the breach than when using large paint.
Originally Posted by bowcycle
As mentioned above, an ideal barrel is one that is 0.003" underbored. That is great if you hand select every ball you will be firing so that they all fit that criteria for your barrel. Since you usually don't select your balls that stringently, you have to select a bunch of balls and then size your barrel for the largest ball in your batch. The problem hear is that the ideal fitting ball will have the highest velocity and the smallest one will have the least velocity, causing inconsistent shooting. So, Overbore your largest ball a bit so that all balls are overbored and that variance is reduced. You give up on efficiency as a whole, but your consistency will still be pretty good, but not perfect. The overbore will prevent barrel breaks in brittle paint as well. So, you won't be sacrificing a lot of consistency, but you will give up some efficiency and you will gain the ability to keep your barrel clean and free from broken ball goo.
Except for the Automag in front, its usually the man behind the equipment that counts.