Run out on my lathe is usually a non-issue, well as long as I do my part. The test blank I drilled a few weeks ago has near perfect concentricty on the start end, and a tir of .002 on the back end. I am not yet a gun smith, but for what I want, in this case, I figured that would be close enuff. For what its worth, I could insert a drill blank into the piece after drilling, but before any OD profiling began, and get an idea on run out that way. Spinning the part in a v-block, on a surface plate, checking the drill blank for runout with an indicator.
This idea began when I was given a test drill at work. OAL is around 10 inches, so I stand corrected, I can go 6.5 inches in depth, from each end if needed. This thing is solid carbide, with thru coolant, I think I ran the part 2200rpm with a feed rate of .005 per rev, which was on the bottom side of the suggested speeds and feeds for the tool. On 4140 pre hard, I got a hole with a shiny finish on the inside. It looked almost like it had been ground. Saddly the 8620 stock I have does not leave as nice of a finish in the hole. Still it is as good as most reamed finishes, and with a little emery on a 12 inch ejector pin, I am sure I can put a glass finish inside the bore. Anyway these drills work great, it takes just seconds to drill to depth, and pull the tool out. When asked if I wanted any, I suggest a .500 and a .625 and I ended up getting 2 of each.
I started setting some things in place today as I left, so as long as the boss stays home tomorrow, I should be ready to sneak it in
If I get a few started, I'll let ya know how they turn out. All I plan on doing is truing up the OD, and getting the holes in.
Andrew