Friday, April 12, 2013

Keeping the goal in sight

Here are a few pics of our peep sight system being installed and regulated to give us the proper point of impact for this Legend chambered for 404 Jeffery.  No matter how well we have done the math I have never found a better way to do the preliminary work other than shooting the rifle. This procedure is done when the rifles stock work and scope mounts have progressed enough to allow us to break in the barrel first. Breaking in the barrel also allows us the find out how well the barrel shoots and with what loads is it most accurate.

Brian will then determine the approximate height for the front and rear sights from the centerline of the bore and then choose his components based on these calculations. He then drills and taps a 6x48  hole at the muzzle end of the barrel, cuts the proper radius on the underside of the ramp and then tightens the ramp in place with a 6x48 screw. A piece of safety tape is also wrapped around the ramp to keep it from flying off a heavy kicker and damaging the ramp. Then he machines the underside of the rear sight base to match the rear bridge radius. The rear base is screwed in place and the aperture is slid into the dovetail. The rifle is then shot at 50 yards with the most accurate loads we found while breaking in the barrel.

You'll note on the target below that the 1st group is way to high. Using a trig function we then determine the amount of correction required to both the front ramp height and rear base. We typically have 3 aperture heights for rough elevation corrections. We use a NECG Universal front ramp and front sight blades as this system offers a wide variety of bead styles and sizes. Once installed this combination allows for simple and accurate elevation corrections.

Based on the point of impact of the first group Brian made the second height correction by choosing a lower aperture slide and some additional machine work on the underside of the rear base. I then went back to the range and shot the rifle again at 50 yards, note the group in the middle. A third and final height calculation and correction was made and a cross section of 4 different loads were assembled for the final range trip. These loads were put together with 4 different bullets and in this case 4 different powders. The velocities of these loads were to approximate the intended final
velocities. This is done to insure that the point of impacts with the different bullets and powders are relatively close to one another so any fine adjustment is still within the elevation limits of the front sight blade adjustment range. The lowest group finds the point of impact for all 4 loads where we want them to be.

With this work complete it is now time to permanently screw and solder the front ramp in place and finish up the cosmetic detail work on the sights.

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