My technique for drilling bolters is to start with a pointed round file. When I drill out the barrel is taken case by case, if the position of the gun is to close to other parts of the model, I'll drill the barrel before assembling.
Step 1 - After cleaning up any mold line across the barrel, I use the point of the file to create a pilot hole. Just a little intention to give my small drill bit a point to rest in. I usually roll the file between my fingers to make sure the mark is well established. I find that I have the most control with the round file for this part.
Step 2 - I drill from the side of the barrel. On the model there is a small depression on either side of the barrel. I don't push all the way through. I drill both sides to roughly the middle. And once the hole is complete then I use the bit like a file to smooth out the bore. Run it back and forth straight through. Do not try to change the angle.
Step 3 - line your bit up with that indent you made on the tip of the barrel in step 1. Slowly drill in until you break the tension into the bore you drilled in sept 2.
Step 4 - clean up the holes using the drill bit as a file like you did in step 2.
When painting make sure you get a little bit of lead beltcher or what ever color you are using for the metal gun bits in the holes while you are painting the rest of the gun. Same goes for the Nunl Oil when you are applying the wash. Be careful not to clog up the hole with either paint or wash. I don't highlight the hole, because I want it to remain dark.
EDIT - You'll get better at this the more you do it. So don't be to hard on yourself for the first squad. And even once you get proficient at this, you are still likely to screw one up in the future. So take your time every time.
Edited by ValourousHeart, 12 May 2021 - 05:04 PM.