1910 Erfurt K98

[jmoore]

Now comes the fiddly bit. Hold the pencil firmly against the cartridge and with the other hand, making sure that the rod is on contact with the case, run down the nut nearest the muzzle until it just touches the muzzle WITHOUT DISTURBING THE OUTER NUT. Apologies for shouting, but this really is the awkward part of the operation.

The witness mark on the inner nut has now shifted. Knowing the thread pitch and observing how much the inner nut has rotated, you can calculate the movement. This movement is the play or "head clearance" for that type of cartridge in that rifle.

If you could maintain light forward pressure on the case, using perhaps a bit of open cell foam or dacron (or an assistant), could you not directly measure at the muzzle without disturbing either nut? Just ease the feeler gage between the nut and muzzle? Perhaps even easier with the addition of a washer or two? Just pondering.