A very specialized gunsmithing job is reboring a rifle barrel to a larger
caliber, let me show you how this is done. Here's an old Winchester 1885 low wall
in the long obsolete caliber of 32 rimfire. This gun was made in 1891 and
the bore is badly pitted. Collectors might call this an old brown gun as all
of the original finish has turned brown and not much collectors value remains.
However it's a good solid rifle and I'd like to shoot it. The barrel will be
rebored and chambered to 357 Magnum but I'll shoot mostly 38 special lead
bullets through it. Since this gun started as a rimfire I'll also have to
convert the breech block to centerfire. The first thing to do is to completely
disassemble and inspect the rifle. I'll remove the sights make sure to drift
them out from left to right. Then using a barrel vise and action wrench I'll
remove the barrel. Reboring is a very specialized gunsmithing job so I'll send
this barrel out to have it rebored. Let me give you a simplified view of the
reboring process. First the bore is drilled and reamed for the larger diameter in
this case from 32 to 35 caliber. After which it's hand lapped to remove all of
the reamer marks. Then new rifling grooves are cut one at a time with
multiple passes to deepen each groove to a depth of about five thousandths. It's
slow painstaking work. Finally the rifle bore is hand lapped to remove all of the
marks left by the rifling cutter. Now that the barrel is back with a brand new
bore I can do my part to finish the project.
I'm chambering it in 357 Magnum using a precision reamer in the lathe. The
chamber end of the barrel is centered in a four jaw chuck using a plug gage
with the muzzle end held in a spider. A floating reamer holder is used to keep
the reamer aligned with the bore. Using plenty of oil
I'll cut the chamber about a hundred thousandths at a time
backing out the reamer and clearing the chips. As I get closer I'll check my
progress with a go gage which should end up just flush with the back of the
barrel. Since the barrel makes contact with the
breech block this will give me the correct headspace. The next step is to
recount the muzzle. I've refixtured the barrel and the lathe for this process
the original crown was flat which I'll preserve just need to remove a few
thousands to clean up the face.
The crown is finished by chamfering the muzzle at the edge of the bore.
I've offset the cutter at 45 degrees to make this cut. The final step is to break
the outside edge of the barrel to do this I've reversed the rotation of the
lathe and place the cutter on the backside of the barrel.
Converting the breech block from rimfire to centerfire involves drilling a
new hole in the breech block and making a new firing pin. The extractor must also
be modified to work with the larger 357 magnum case. For posterity reasons I'll
mark over the original caliber and put the new caliber marking on the left
barrel flat. I'll also leave a message of the work I've performed on the bottom of
the barrel under the forend the old finish must be removed for the marking
process to work I'll use some tape with the correct shapes cut out and simply be
blast off the old finish.
The marks are made using the machine from marketing methods. It uses a process
of electrochemical etching. I've printed a stencil that just needs to be taped to
the barrel. Touching the marking pad to the barrel edges the mark through the
stencil.
A bit of plum brown will touch it up and after putting it back together I'll head
for the range.