Itís a fantastically complex and demanding task, and the barrel
makerís attention to fine detail is extremely important to good future
accuracy. You can have the most highly engineered action, the most
expensive stock, the most sensitive of triggers, and a well proven load,
but if theyíre matched up with a so-so barrel, youíve got problems. All
that aside, the more you know about barrel making, the better the
questions you can ask when shopping for your next re-barrel job. Letís take
a look at how it all gets done.
The steel for rifle barrels comes from various small specialty
mills and is often delivered in 20 ton lots, which is a tiny amount by
regular steel mill standards. The delivered bars can run anywhere from 12
to 20 feet in length and are usually 1.25" in diameter. Additionally, they
may or may not be stress relieved at the mill and their chemical
composition and quality may or may not be certified (depending on whether
the barrel maker wants to pay for it). However, it is extremely important
that only the highest quality steel be used for barrel making. That means
that there are absolutely no voids in the material, no carbide crystals,
nodules, or other impurities embedded within, no soft or hard spots, and
the steel is perfectly homogeneous throughout.
Barrel steel should have three basic characteristics i.e. machinability (the ability to be easily cut and shaped), durability, and
strength. The two kinds of steel that are used most often for rifle
barrels meet these demanding criteria. One is 4140 chrome moly steel which
is a type that is most commonly used in high stress applications such as
in truck axles and various bulldozer parts, etc. The other is 416
stainless. This type of steel is not your ordinary stainless variety.
While it contains 10% chrome for corrosion resistance, it also contains
sulfur to improve its machinability. Like chrome moly steel, itís also
capable of being heat treated to increase its hardness to make it even
more strong and durable.
Obviously you can overdo the hardness to the point that the
steel can become brittle, so typically most barrels, no matter what the
material, will run between 25-32 on the Rockwell scale. This means that
their strength will be able to handle pressures of at least 100,000 psi.
If you need a barrel that can handle an even larger amount of pressure,
you should change your load.
After delivery to the barrel maker, the bars will then be cut to length
(around 28-30") and then trued up so that theyíre perfectly round and the
ends will be faced off. Having a perfectly round bar and perfectly
parallel sides is extremely important as youíll soon see. Then, if the
bars have not been heat treated at the mill, theyíll be heat treated to
remove the stresses induced into the barrels from the steel making
process. This usually involves baking the bars in ovens at around 600
degrees centigrade with a slow, controlled cool down taking anywhere from
12-24 hours depending on the chemical composition of the steel.
This is definitely the most difficult part of the whole process.
Ever try drilling a long, straight hole? Itís not easy. It always seems
like the drill bit never comes out in exactly the place that you intended.
Here, weíre talking about drilling a relatively small hole for thirty
continuous inches in some very hard material. However, barrel makers have
come up with a very unique approach to this problem.
They mount the barrel in a fixture and then spin the barrel at
anywhere from 2-6 thousand rpm. The drill bit is stationary and is mounted
on a 40 inch rod that is then moved into the spinning barrel at a rate of
around an inch per minute. As you can see this is a slow process.
The bit is made from tungsten carbide steel and is shaped with a
cutting lip on only one side of the tool. I know it seems strange, but
thereís a reason for it. Both the drill rod and bit are hollow and cutting
oil is forced through them at anywhere from 1,000-1600 psi to flush out
the resulting chips/swarf. Because the bitís cutting surface is on one
side only, room is left on the opposite side for the metal chips and oil
to flow back out of the hole being drilled.
You can see why having the barrel perfectly trued and round is vitally important if itís
going to be spun up at these very high speeds. If it weren't, itíd be
wobbling, or perhaps even flying all over the place. Even a very slight
imbalance would have serious consequences as it would cause the barrel to
bow as it was being spun. That means while you could drill a straight hole
in a bowed spinning barrel, when you stopped the spinning, the barrel
would then straighten out but now the hole would be bowed.
Another problem the barrel maker has to confront is making sure
the drill bit, which is soldered on to the drill rod, is perfectly
straight and true. If itís not, the hole wonít be straight. Additionally,
they have to make sure the bit is perfectly centered on the barrelís
center and that the bit wonít wander, flex, or chatter as itís being moved
on that long 40" rod into the barrel. Lastly, your machinery has to be in
tip top condition. Any wear on the high speed precision bearings of your
gear will translate into an inaccurately drilled barrel. As they say, the
details will get you every time. Barrels are usually drilled around .005"
under the desired bore size, which brings us to reaming.
Even though the barrel maker has taken great care in drilling
process, the surface finish of the hole wonít be as smooth as we would
wish. This is where reaming comes in. The reaming process will bring our
barrel hole up to final bore dimensions and will provide us with the final
finish of the surface (unless we have the barrel lapped).
In this case, the barrel is now stationary and itís the reamer
that is rotated. The reamer is located on the end of a long shaft which is
then spun at 500 rpm. The barrel is now moved forward onto the spinning
reamer. Both the reamer and the shaft itís mounted on are hollow, and as
before, cutting oil is pumped through at 200 psi to cool, lubricate, and
flush out the swarf.
As before, itís critical that the reamer and the barrel are
perfectly aligned and that the reamer and its rod wonít flex, wander, or
chatter. If this operation is done properly, weíll have a very smooth
hole. If not, weíll have horizontal marks around the diameter of the bore.
In my examination of many, many barrels over the years with and without a
bore scope, this is the most common barrel flaw that Iíve found. Custom
barrel makers do an excellent job in reaming. Barrels on mass manufactured
firearms often will have reamer mark on tops of the lands and sometimes
even in the grooves. I would guess that poor maintenance of the reaming
tools is probably the biggest culprit for this situation. Now itís time to
rifle the barrel.
Cut rifling is the oldest of the various types. It was invented
in Germany in 1492 - a very good year for more than one reason. As the
name implies, a cutting, or maybe a better word might be a shaving tool,
scrapes away the metal in a spiral pattern to form the grooves of the
barrel. A cutter hook is mounted in a "cutter box" or carrier
which fits inside the bore. Like a wood plane, the cutter box is pulled
through the barrel shaving away .0001" of metal. After itís pulled all the
way through, the barrel is rotated and the cutter box starts shaving the
next groove. After all six grooves are done for the first time, the
cutting hook is adjusted another .0001" lower and a second, third, etc.
pass is made until the desired depth of the grooves is achieved.
As you might guess, this is a slow process, and it takes
somewhere around an hour to rifle a singe barrel. It also takes a very
skilled operator to run and adjust the machinery. Consequently, cut rifled
barrels are more expensive to produce than the other types. However, on
the plus side, the barrel incurs absolutely no metal stresses what so
ever. Indeed, cut rifle barrels like those from Krieger, have produced
remarkable results on the benchrest circuit.
Button rifling was perfected during World War II when it became
clear that the slower cut rifling methods of the day couldnít satisfy the
tremendous demand for barrels. The process was perfected by Remington who
used the nearby facilities at Hart Barrels for its experiments during the
In this process, which is the most common in the U.S., a carbide
"button" is passed through the bore to form the rifling. First the bore
has to be lubricated. Every barrel maker has their own "secret sauce" or
lube and guards its identity fiercely. A button is a somewhat football
shaped carbide tool with the rifling pattern ground in relief into its
surface. The button is attached to a rod and is then pulled through the
bore. (Hart pushes them through instead.) As the hard button passes
through, the raised rifling pattern on its surface is pressing into the
softer surface of the bore and is creating the grooves in a cold forming
The operation is very fast, and only takes about a minute per
barrel. Thus, button rifled barrels are usually less costly to produce.
There are two types of buttons. One is a simple rifling button which works
as just described. On the minus side, a simple button will leave burr like
feathers on the edge of the lands. However, a combo unit which consists of
a rifling button and a finishing button will both press in the lands and
smooth their edges in the same pass.
As you might guess, pulling an oversized button through an
undersized hole requires great force and creates significant stress in the
barrel. As a result, itís mandatory that button rifled barrels be stress
relieved after the process. If not, all kinds of strange things including
splitting down the length of the barrel is possible.
Again, it was the demands of war that was responsible for the
development of this process - only it was done by the other side. Hammer
forging was developed in Germany in 1939. Here a drilled barrel, rather
than being reamed, is honed to give it a very fine interior finish. Then
it is placed on a tungsten carbide mandrel that has the entire rifling
pattern ground in relief into its surface. The barrel/mandrel combo is
then placed between two opposing power hammers and rotated. The hammers
literally beat the barrel into the mandrelís pattern. Iím told a barrel
will actually grow around a third of its length during this process. It
usually takes around three minutes for the rifling process to be
completed. As you would think, this method produces tremendous stresses in
the barrel that have to be relieved through heat treating.
The advantages of hammer forging is the fact that the interior
finish is very good, and the bore surface becomes work hardened in the
beating process. The result is a very durable, long lasting barrel. Modern
hammer forging has progressed to the point that even the chamber can be
included in the mandrel pattern. These machines are very large, complex,
and expensive however. So the small custom barrel shops are pretty much
eliminated from using them.
Additionally, some say that the induced stresses are so severe in this
process that they never can be entirely eliminated. As a result, the bench
rest crowd wonít touch a hammer forged barrel. However, I canít help but
wonder how valid this belief actually is, and whether anyone has actually
tried it. Remington barrels, which always had a reputation for accuracy,
used to be hammer forged, including those used in the XP-100. I know I
always had excellent results with original XP barrels. Indeed, in Europe,
hammer forging is the standard. Sako, Tika, H&K, Steyer, and Sauer all use
hammer forged barrels. Iíd hardly call their products junk.
Most premium barrels are lapped. The unanimous verdict of just
about every expert in the barrel making arena is that lapping does indeed
improve accuracy. Lapping accomplishes this by polishing the interior
surface smoother and eliminates any tight spots in the bore.
Lapping is generally a hand operation. A rod with a handle at
one end is inserted into the new barrel. Molten lead is then poured down
the muzzle around the rod for a distance of around 4". The lead then
hardens and the lead plug or lap is tapped out. The lap now has the
perfect relief pattern of the interior of the bore. Lapping oil or lapping
compound is placed on the plug which is then passed back and forth in the
polishing process. An experienced person can readily feel any tight spots
and then work to eliminate them to produce a near dimensionally perfect
bore. Again, all this hand work costs money, so only the very top quality
barrels will be hand lapped.
Now you might be thinking, "Well I can improve the accuracy of
my unlimited gun by lapping the barrel my self". Donít do it. Lapping will
increase bore size. The barrel maker has already taken this into account
when ordering his buttons so when he laps, the final diameter will meet
Lapping a mounted barrel will especially increase the bore
diameter at both ends of the barrel. This isnít a problem for a new barrel
since one end is going to be crowned and the other chambered. However, on
an existing mounted barrel which already has a chamber and crown, throat
diameter will be enlarged and so will the muzzle. This is especially
critical at the muzzle because itís very possible that the bullet wonít be
fully supported when it exits and will tip and yaw excessively as a
result. Accuracy is likely to be very poor.
Let me end this piece by making a comment about breaking in a
new barrel. Iíve written about this in the past so I wonít repeat the
details of the process and will just say that if you want the very best
accuracy that your barrel can deliver, you should take the time to follow
a break in procedure. Why? Because even the very best barrels will have
small imperfections on top of the lands and in the grooves. When you
follow a break in procedure, youíre giving your barrel a final polish that
will smooth out these imperfections, and your new barrel will be shooting
its best in the least amount of time. Accuracy reducing fouling will be
also minimized. I know itís a pain, but itís a good investment in future
So there you have it. If you keep this information in mind when
shopping for an aftermarket barrel, youíll be more likely to make the best
choice for your needs. A good barrel is like a good dog. They give so much
pleasure that youíll remember them long after theyíre gone.