[Unclenick]

Mtnsmith,

Hatcher intentionally increased headspace to something like 1/8" in the .30-06 and still didn't blow caseheads on the first firing. What you could have done was use a case comparator, like the RCBS Precision Mic or the one for the Hornady L-N-L gauge and measured the cases before and after. You can pretty well guess that if they didn't grow more than 0.008" that everything was in field go gauge spec.

BTW, if you find you need to have the headspace corrected, lap your lugs first (an accuracy step, but something easy and a good idea to do with a non-original bolt to assure the lugs fit properly), as the metal you take off will grow headspace.


Jim,

As I expect you already know, but for the sake of others reading the thread: SAAMI specs can show maximum case lengths at the shoulder that are longer than minimum chamber dimensions. Because a chamber is wider than the maximum cartridge diameter, the bolt of a conventional rifle action is expected to be able to close on and squeeze the cartridge a little shorter and fatter to fit if needed.

The TC actions don't have the camming of a bolt locking lug or the leverage of a bolt handle to assist in closing on a long case. So in their case, as with NATO chambers, interference fit is not allowed. Insuring no interference is where that 0.001" gap for TC chambers comes from. Another factor may be that number of benchrest shooters say they find that bumping shoulders back 0.001" shorter than the chamber rather than strictly neck-only sizing, produces better accuracy.

So I expect one or both of the above considerations are at play in the statement regarding what headspace "should" be. But as with all things gun, YMMV. I would not, for example, run a gas gun chamber that tight. Too much chance of encouraging slamfires or getting feed jams.