If you drill the bar you have to drill both sides (you will occasionally need to flip the bar) as you want the oil delivered on the outfeed side of the nose otherwise it just gets thrown off the nose.
I drilled a couple of bars but then gave up on that method because the holes eventually get blocked. Now I just "wick" the oil direct onto the line where the chain rides on the bar. This means locating the wicking point as close as possible to the bar/chain.
This photos shows two oiling points- the Thru bar oiler is a hole drilled in the bar.
Then a hollow bolt with a hole in the side lined up with the bar gap,
The top one uses a hollow brass bolt within a 1/64"of the bar/chain.
Brass is used because if it vibrates loose it won't change anything.