OBERMEYER RIFLED BARRELS 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 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 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.