Thanks Stwert, I was searching for them myself...

I explored putting holes in cylinders a couple years ago. The idea was to create the clean topology in a plane and then use the bend deformer to roll it into a cylinder.

Here is a link to the thread.

https://simplymaya.com/forum/showthread.php?t=33378

There are a couple of video links in there that demonstrate the process.

I made a couple versions as I explored different ways to lay out the topology. These were made a couple years ago and I was just figuring out how to use camtasia and they were not meant to be polished in any way.

Here is a topology that has a punched hole affect...

maya holes in cylinder tut wNarration - YouTube

This is a method that produces a more uniform drilled and smooth affect...

hole in cyl tut2 web - YouTube

and here is a muzzle break example that uses a boolean approach ...

muzzle and heat sync final - YouTube