barrel shoulder, and set the micrometer carriage stop against the forward end of the lathe carnage.
Next, back off the micrometer stop the required number of thousandths of an inch for one revolution of
the barrel, less the amount required to make the marks on receiver and barrel meet. This number of
thousandths of an inch is then deducted from the number of thousandths of an inch the barrel moves in a
full revolution. The answer is the amount the micrometer stop is to be backed away from the lathe
carriage.
A thread must be machined from the rear end of the barrel, on such barrels, which have a shank section
at the rear machined to a diameter of the root diameter of the thread.
If the rear end of the barrel is slotted for an extractor, this slot must be deepened. This is done while the
barrel is still in the lathe, using a tool post grinder, with a grinding wheel narrow enough to enter the
extractor slot, or done on a milling machine. It may also be done on the milling machine.
This method of bringing a barrel to its correct place in the receiver when it screws past the register mark
can only be used if a chambering reamer is available. After shortening the barrel at the breech end the
chamber must be deepened the same amount.
If no chambering reamer is available, instead of shortening the barrel so it can be seated one turn
deeper in the receiver. A steel shim must be placed between the barrel shoulder and the part of the
receiver against which this shoulder bears. When using steel shims, lubricate it either with oil or colloidal
graphite to prevent it tearing under the twisting pressure.