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July 25th, 2008

McGowin Shoots 300-yard Record Group

Shooting in the Unlimited (rail gun) class, James “Jim” McGowin shot a 0.355″ 5-shot group at 300 yards. This has now been officially “certified” as a new NBRSA record. McGowin’s group beat the previous 0.373″ shot by Art Freund in 1981. McGowin was shooting the 6mm Beggs cartridge in a match in St. Louis, MO. For his record group, Jim used his own 63 grain BT bullet, a 7.5 ogive made on J-4 .750 jackets in a Niemi die.

The 6mm Beggs cartridge is basically a 220 Russian necked up to 6mm, with a very small modification of the radius at the neck-shoulder junction. (Gene Beggs added a tighter radius to reduce case lengthening on repeated firings.) The 6mm Beggs, and its smaller cousin, the 220 Beggs, have slightly less capacity than a fire-formed PPC case. However, in a good BR gun, the “raw accuracy” of the Beggs’ cartridges can rival that of a 6 PPC. Indeed a standard, unmodified 220 Russian is competitive in the 100/200 yard BR game. Lou Murdica, a top shooter on the short-range BR circuit, has won many matches with a “plain-jane” unmodified 220 Russian.

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July 25th, 2008

Tuned Windage Compensating Knob from Kenton

Kenton Calibrated Windage KnobHere’s something that can save you lots of time and aggravation on a varminting trip. This little $70 gizmo is great for varmint hunters and any one who needs to make a quick shot in shifty wind conditions. Instead of the traditional 1/4-MOA hash marks, the Kenton windage turret features markers corresponding to the wind drift your rifle will encounter at various distances.

Kenton Industries’ Tuned Windage Compensator (TWC) has built-in windage marks for 10 mph cross-winds at 100-1000 yards. How do they do that? Well the knobs are calibrated either for specific calibers/loads, or they can make custom knobs using your observed field data. The knobs can compensate for various wind speeds (2-20 mph) and angles (15°- 90°), by applying some simple conversion ratios. As a general rule, with a “full-value”, i.e. 90°, crosswind, the wind drift will go up or down in direct proportion to the change in windspeed. That means, for example, at a given distance, a 10 mph crosswind will push the bullet twice as much sideways as a 5 mph crosswind.

Two versions of Kenton’s TWC knobs are offered. The $69.95 TWC #1 features calculated ballistics for your caliber and barrel length. The $79.95 TWC #2 or #3 feature customized windage settings based on bullet BC, environmental conditions, elevation, and ballistic information you provide.

Kenton also makes an elevation-compensating TTC knob, that can be customized to your rifle. With this elevation turret, yardages are marked in 50-yard increments, and you can literally just “dial in your distance”. However, to work effectively the TTC knob must be tailored to a particular load (velocity and bullet). Moreover, actual bullet drop will differ with changes in altitude, temperature, and shooting angle — so it’s not as simple as it sounds, and you may need multiple knobs if you shoot a variety of loads.

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