Drilling holes in barrels without kicking up huge burrs is not casually done. This is not conducive to maintaining rifling. Manufacturers use EDM machines (Electrical discharge machining) which remove material without cutting it. I should mention that I have a Webley barrel that has a couple of holes down through the top of it, but I have no idea how this was accomplished without kicking up burrs. Perhaps they were removed after the fact, but I don't know how. They don't seem to interfere with the barrel's function, though.
The other method is to machine an expansion chamber on the end of the barrel, and cut ports in the top of that. The ultimate recessed barrel crown. If you're going to try a home porting job, this is probably the route to go, but it requires enough meat in the barrel to accomodate the expansion chamber. And a lathe, with appropiate tooling to hold barrels. Additionally, it requires dismounting revolver barrels, but maybe that goes without saying.
Note: I've tried none of these personally, I'm just relaying what little I know.
Yer on yer own at this point, pilgrim.