Quality Rifle Barrels Since 1962

23122 - 60th Street
Bristol, Wisconsin  53104

Frequently Asked Questions (FAQ)
What is your current situation with regard to fulfilling orders?

I am a one-man shop, and I have been involved in a lot of defense work for quite a few years. The
volume of this work has been reduced, permitting a greater focus on civilian orders. However,
such non-military work tends to involve only 1 or 2 different barrels per order, meaning there are
more frequent changes in machine set-ups.

What is the relationship between the cut-rifling process, rifling depth, and barrel life?

Bullets are driven by the lands. Through many years of experience, I have found that a greater
depth between the lands and the grooves means the resulting barrel will last much longer at a high
level of performance. Manufacturing limitations pretty much confine this long-life performance
characteristic to cut-rifled barrels. In order to achieve the necessary additional depth, the cut-
rifling process uses different tools and involves more time than the methods used in the high-
volume production of factory barrels.

What are your typical bore diameters, and what are your installation recommendations
regarding reamers?

The installer needs to be able to pilot his reamer with respect to the dimensions of each barrel. I
recommend a removable-pilot reamer so the installer can also work with conventional diameters
standard to other rifling processes. (In addition, some other barrels are simply manufactured large,
and the removable pilot allows the installer to correct his reamer to work on them.) It should also
be noted that pressure does not jump simply because the land diameter is tighter; it is the cross-
section area of the entire bore that counts. My 5R system often results in a larger cross-section
area than many shallow-rifled, wide-land conventional barrels. Special bore sizes associated with
various typical calibers are as follows: .217" (.22 caliber center-fire), .234" (6mm), .254" (6.5mm), .
274" (7mm), .298" (.30 caliber), .300" (.303), .311" (8mm), and .328" (.338). Pilot sizes are calculated
by subtracting .001" from the bore diameter.

What was the original purpose of having a tight groove diameter, and how have circumstances

The idea has long persisted that a tight groove diameter works better, particularly in a Palma rifle.
In part, this perception resulted from the past use of under-size bullets in certain Commonwealth
countries. However, all currently-manufactured Palma bullets I have checked are now .3080" or
larger, and I no longer make tight-groove .3065" barrels. I now make Palma barrels with a minimum
diameter no smaller than .3075".

What is your philosophy regarding groove diameters?

Generally speaking, I have found by experience that a diameter of about .0005" larger than nominal
is better. Metal deformation occurs in accordance with the principle of volume constancy. This
means the bullet is forced to undergo strain along its axis (lengthwise) to compensate for the
volume of material displaced by the lands. As noted previously, even though my 5R cut-rifled
barrels have a greater depth between the lands and grooves, the remaining cross-section area
between the lands (not requiring deformation) is often greater than in many shallow-rifled, wide-
land conventional barrels. However, having a tight groove diameter restricts and compresses the
bullet to an even greater extent in the radial direction, thereby creating additional, unnecessary
deformation. Maintaining a larger groove diameter, on the other hand, reduces bullet distortion. I
have found several instances where barrels having groove diameters .001" to .002" over nominal
actually proved to shoot extremely well. One of these cases involved .30-caliber barrels I made
with groove diameters of approximately .3095" for a gun writer who intended to shoot cast
bullets. When he ran some tests on jacketed bullets, this set of barrels turned out to be at the
top of his list for performance with bullets like the Sierra 168.

How important is uniformity of twist rate, and how do you control it?

Uniformity of twist is definitely important, and the Pratt & Whitney hydraulic rifling machines
allow it to be consistently maintained. The twist rate is controlled by change gears, which transfer
the twist to the tool spindle from the master leader bar. This results in extremely uniform and
repeatable twist rates. I also have gain-twist leader bars, but I only use them for ordnance work.

What does it mean when a barrel is said to be a "5R"?

5R is the form of rifling I developed for use in most target barrels and in many sporting barrels.
These barrels have 5 grooves, and the lands have angular sides. I have observed that bullet jackets
will deform such that they remain closer to the R-form lands than they will to the sharp-edged
lands present in conventional-style rifling. This reduces powder fouling at the corner of the
grooves. The angled form of the lands also helps to reduce jacket failures in quick-twist barrels.

If I am interested in ordering a barrel, should I send money now?

No, please do not send money with your order. Billing will occur when your barrel is completed.

How may I contact you to place an order or to make further inquiries?

Please place all orders in writing, even if you have already done so verbally. This will help ensure
that we have a hard-copy record of your order and all of the necessary details. The address and/or
fax number for doing so is as follows:

    Obermeyer Rifled Barrels
    23122 - 60th Street
    Bristol, Wisconsin  53104

    FAX: (262) 843 - 2129

It is hoped that this web site will offer an option to address more frequently asked questions in a
manner that is accessible to everyone, allowing for a more efficient use of production time.
Nevertheless, if you do not see an answer to your particular question in the FAQ, or if you desire
further information, please feel free to make an inquiry by telephone at (262) 843 - 3537, during the
day, Monday through Friday.