The basic techniques of getting rid of the "dimples" are:
Drill them out with a 1/4" drill, then polish the inside of the tube to make sure all traces are gone.
The holes are completely covered by the barrel's support ring when the gun is assembled.
One poster uses an appropriate socket from a socket wrench set as a "ironing" tool to press the lugs out, then polishes inside.
Once you have the dimples pressed out, you can use a small steel hammer to gently tap the dimples flush by inserting the socket into the tube as a support.
Grind them out with a Dremel or flex-shaft and abrasive tips.
Have a gunsmith use a shotgun hydraulic dent remover tool to press them out.
And variations on the above methods.
Whatever you use, you MUST be 100% sure to polish all traces of the dimples or any remaining burrs out, or the follower or shells will hang up in the tube, causing a stoppage.