It may vary by brand, but the SDM made front sight I used to replace my pinned in sight on my S&W 686 didn't come pre-drilled. It fit so tight in the slot for it that I pressed it in using my vise and I didn't bother to drill and pin it in. It has held so far. I have read, if you are installing the pin, to drill it halfway thru from each side of the barrel to avoid popping out the opposite side offcenter. My original sight was really tight in the slot as well and I also had to use the vise, padded of course, to grip the sight and pull it out.