Probably the worst esperience I ever had AS a gunsmith was installing a set of irons on a thin barrelled rifle. I should have silver soldered that front sight on, but had used up the last of it the day before, so I went with screws (which the customer wanted anyway - so he could remove it if he wanted to) .
Well, I put that front hole right through the barrel into the bore, so ended up shortening his barrel by 2 inches. Most embarressing, and another freebie. He was kind enough to accept this solution, rather than costing me a replacement barrel. His choice.
If you don't screw up once in a while, you aren't trying hard enough.
