Stretching Brass with a Lathe
If you’re fortunate to have a lathe or a friend that has one, brass can be
lengthened using a “nib & spin” technique. The process involves the use of a die
to hold the case and a “nibbing rod”. The nibbing rod is similar to a boring rod
but has a very smooth hardened bump on one side close to the end, or has a
hardened ball bearing seated on one side to form the bump.
A die, similar to a full-length resizing die, is constructed to rigidly house the case and
keep it from turning inside the die. The die inside diameter (ID) must closely match the
outside diameter (OD) of the case. The die and case are aligned and clamped in
the chuck jaws. Once everything is setup, the nibbing rod is inserted deeply into
the case at a point where the case wall is thicker.
As the lathe is running the nibbing rod is adjusted so that the bump or ball bearing
presses against the wall of the case and slowly “irons out” or thins the wall as the case spins
and the rod advances towards the case mouth, hence the term “nib & spin”. As the wall is
thinned the excess brass is forced forward lengthening the case.