[Unclenick]

Thedaddycat,

There seem to be two lengths now involved in the discussion here. The length of the neck off the shoulder and the length from bottom of the case head to the shoulder datum intersect, which the sizing operation controls prior to trimming.

For the first consideration, sticking to the SAAMI minimum difference between the case neck and chamber neck for any particular cartridge will be adequate by by definition. For 6.5×55, specifically, that will mean making the case neck 0.0122" shorter than the chamber neck. But frankly, 0.010" is a number used in other chamberings and will be fine in any scenario I can dream up, if you prefer to use it. If you chamber gently so the chamber never sets the shoulder back any further, you could go even shorter, but I don't think any measurable benefit will result.

As to shoulder setback, neck-sized-only cases will fit and fire several times before they need to be resizing at all, except periodically when they get tight. Glen Zediker and others commonly recommend 0.002" shoulder setback by a sizing die for reliable rapid feeding, especially in semi-autos. A lot of benchrest shooters use 0.001" setback, feeling it self-centers slightly better than neck-sizing-only, but keep in mind they load singly rather than from a magazine, as a rule. You can experiment with these loading approaches for yourself. They all assume you start with a case that fits in your chamber easily for the first fireforming, as Mr. Guffey described.