Alright, so if you're observant then you've noticed that my Space Marines and Orks have barrels with perforated muzzles, while none of my goblins did. This is because, as far as I know, all second edition models have solid tips on the guns, and I imagine that you would have painted a black dot to signify the muzzle.
However, this isn't an option for me, thanks to my trusty friend Mr. Tamiya Fine Pin Vise and his associates.
So today we're going to be using the 1.5mm bit on these unsuspecting goblins.
First you line it up and drill-
Finally here are some shots of my results with a SM Sergeant's bolter pistol, since the effect is easier to see.