Re: Obermeyer
Here's his FAQ page.
OBERMEYER RIFLED BARRELS
Quality Rifle Barrels Since 1962
23122 - 60th Street
Bristol, Wisconsin 53104
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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 during the last 3 years.
This work has been growing and has priority over regular civilian work. Since I currently have
machines set up to run .30-caliber barrels with 1 in 11" twist for my defense work, that is also the
type of barrel I can most readily make for the civilian market at this time. I have also been making
some 1 in 13" twist barrels to support requirements for Palma rifles and magnums, as well as 1 in
12" twist barrels. In addition, I have been able to make some 6.5mm barrels with a 1 in 8-3/4"
twist, commonly used with .260 Remington chambers, for example, and now make some with a 1
in 9.1" twist for large-capacity cases like the 6.5mm x 284. Small-diameter barrels, such as .22
caliber and 6mm, have been the most difficult to fit into the production schedule.
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. <span style="font-weight: bold">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), and .311" (8mm). The 7mm bore
diameter has been .2755" in the recent past, and legacy barrel blanks of this type may still be in
circulation. Pilot sizes are calculated by subtracting .001" from the bore diameter.</span>
What was the original purpose of having a tight groove diameter, and how have circumstances
changed?
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 the tight-groove .3065" barrels. I now make Palma barrels with a
minimum diameter no smaller then .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 that 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 bullet 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 the twist rate, and how do you control it?
Uniformity of twist is definitely important, and the Pratt and 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 corners 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:
It is hoped that this web site will offer an option to address 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 the 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.
