Smoothing Out a Cob?

Sandpaper.

A rotary tool, unless you know exactly what you are doing, is probably too aggressive. I'd recommend trying them as is, sometimes, like a rusticated or blasted briar, that feel will help you grip it and keep it in hand. As you smoke it the roughness will smooth a bit.

You're welcome. Like I said, smoke it and see how you like it after your hand smooths it after a dozen or so smokes. I clench, so it doesn't do as much for me. But if you fondle your pipes a bit, it may do a lot.

My favorite stock MMs are actually the ‘naked’ versions. Of course, they have completely rough bowls. Maybe it’s just my imagination, but they seem to smoke easier & cooler to me.

olkofri, I like to do corn cob modifications as a hobby on occasion. Here are some tips I have learned along the way.
If you want to smooth out the rough natural texture on your cob here are two ways that have worked for me.
You could get some plaster of Paris and fill in all the spaces where the corn kernels where. then sand it smooth.

After that coat pipe with shellac to get it shiny and very smooth. when done it will look like any other MM pipe.
I also have watered down white Elmers glue to get it thin and paint it on the natural cob's to fill on the kernel spaces.

this will take a couple of coats. I then sand it smooth with a 200 grit sanding sponge. I like to use those over sandpaper

because they contour around the pipe.

If you do not want to fill in the kernel spaces spray a touch of clear coat paint or shellac. then sand it a bit. go with 200, grit then 400 grit then 800 grit if you want a shiny finish.
I hope some of this info helps you!

I have sanded most of my cobs with 600 grit. Just enough to smooth out the factory finish. I think it gives them a higher quality feel.