Sign 5 - Boresighting Range

This boresighting range was constructed by Gaasland Construction Company in the fall of 1944 and was used for test-firing fixed guns on aircraft. The tie down anchors placed in the concrete boresight platform still exist. The anchors were used to hold the aircraft in place during test-firing. Two anchors were used to secure each wing and one anchor secured the tail. The range was 1,000 feet long by 50 feet wide with a slope of 6 inches per 100 feet and was once lined with an 8 foot guard fence. 

Boresighting Range

Slight Axis & Bore Axis

Looking down the firing range corridor you can still see the Bullet Stop, a mound of dirt and sand used to stop bullets. Even if you know what to shoot, where to shoot, and when to shoot, it is to no avail nothing if you do not know where your bullets are going when you aim your gun and pull the trigger. The purpose of sights is to tell you where you are shooting. However, sights can't perform this function unless they are aligned with the bore of your gun in such a way that your sight axis will intersect the bore axis at some given distance. Bore axis is a line through the bore of a gun extended into space.

The process of aligning the sight axis and bore axis so that your gun will shoot where you are sighting is called boresighting. To complicate matters more, aircraft with two or more guns had to align their bores on a single sight axis. And we cannot forget that the ever present effect of gravity needs to be taken into account.

Range Construction Notes

Site Area

  • Boresight platform must be constructed 5 feet above the level of the toe of the bullet stop as shown in the section above and the area between shall slope uniformly from platform to bullet stop.
  • Remove all trees, stumps, etc. as noted on site plan.

Firing Point

  • Provide a concrete platform 50 feet square and 6 inches thick. Subgrade to be well compacted earth or undisturbed subsoil brought to a trim grade.
  • Provide expansion joints in paving as indicated.
  • Wheel stops, tail jacks and wing jacks to be provided by others.
  • Malfunction area to be of gravel.


This structure design is left to individual desires of officer in charge and will vary with type of plane used. Target should be movable and mounted up on a base of sufficient depth (say 10 feet horizontal) to allow target to be adjusted a distance of about 5 feet thereby permitting the fixed distance between guns and target to be maintained with various types of plane gun mountings. The target structure will be provided by U.S Navy.


Provide fence and gate as detailed and specified. Its purpose is to prevent personnel from walking between guns and target.

Bullet Stop

Designed for 50 caliber and 20 millimeter ammunition.

Jeep Road

Provide 10 feet wide jeep road of gravel as indicated.

Bullet Stop Construction Notes

  • Sand fill to be loaded into ricochet box at rear end (2 feet deep) first then proceeding toward the front (1 foot deep) end
  • Sides and bottom of box to have 2 coats of liquid hot asphalt.
  • Bore 1/2” holes at 2 feet O.C. in bottom at rear of ricochet box to drain onto rear of rip-rap slope (cover with three-quarter inches of gravel to prevent loss of sand.
  • All exposed and buried woodwork shall have one coat of creosote brushed on, as approved.
  • All earth and sand used for fill construction shall be of select quality, as approved.