You are confusing the baffle and the muffler extension.

Virtually all mufflers have a disk or cone shaped baffle to help reduce the noise and to increase the back pressure. Removing this baffle can give you some increase in rpm, but may result in a slightly harder to tune engine. If you have considerable experience with engines, you shouldn't have any trouble.

The shiny extension is a different thing. Larger displacement engines need a muffler with a larger volume. Rather than make a new casting die, most manufacturers have taken to adding volume by adding an extension in the middle and using a longer center bolt. Your .52 muffler is more than likely exactly the same casting as a .46 muffler with the extension adding the needed volume for best power. You'll see some .75s and .91s using a .61 muffler casting with the extension.

If you use the OS muffler, or take the extension out of the ASP muffler, you may notice a small drop in rpm on the same prop.