Depends on the Bullet
The current crop of popular Benchrest Bullets can vary in size from a flat .2430 to as big as .2437.
I always try to shoot for .0015 overall clearance when measuring the loaded round at it's largest point. On typical flatbase bullets, this will be where the base ends up in the neck.
Bruno Boattails have no "gas ring", and will measure about as close to a flat .2430 as you can measure when checked at the junction of the boattail and the shank. Using this bullet, if you want .0015 clearance in the neck, then the wall thickness should be .0123.
Most Flat Base bullets, and the Barts Boattail, do exibit a "gas ring". you should take an extra .0002 from the wall thickness to compensate.
These numbers are very difficult to measure, that is why you should do what Jerry says and measure the loaded round. Keep in mind, when using the wall thickness method, any error is doubled in the finished product. Sure, you might sacrifice a couple of cases getting it dead on by seating and pulling bullets, but once set, the neck turner will stay there, unless you do something to cause it to move, (like drop it).
I have measured various cases from various shooters, and most are not working near as close as they think. We tend to be rather non-chalant in tossing that "tenths" thing around. The fact is, many can't even use a set of Micrometers well enough to consistantly measure at that level.
Don, I can answer your question. Russel was not heavilly invested in the .262, (just one barrel and a bushing), so he decided to go with the .269, mainly for ease in turning........jackie
