Universal Precision Test Fixture for Firearms

I have spent a lot of time testing the precision of common firearms. As I have been explaining for years, it takes a lot of shots to get statistically significant measurements of precision. And I wanted to be able to collect large samples without wondering whether I as a shooter was introducing variance in the results.

In order to remove the shooter from the equation, precision ballistics researchers going back as far as Franklin Mann in the late 1800s have used “V rests” to clamp barrels to benches.  I wanted to do the same, but with a wide variety of modern firearms, and without disassembling them. So ten years ago I built two “test rigs” with the following design objectives:

  1. Securely hold any gun with a scope rail;
  2. Allow the gun to be loaded, unloaded, and fired while attached;
  3. Precisely return the firearm to the same zero after every shot.

Here are photos of the first version:

With a gun clamped in the fixture, I can precisely align it with the same point on the target for every shot, and then fire it while touching only the trigger. Both versions consist of:

  1. A Lower Frame supported on the bench with three Screws to fine-tune the point of aim.  To maximize their turning precision, the inserts use class 3 threads, and the end of each screw is turned to a sharp point.  The Lower Frame is tall enough to hold any man-portable gun with a magazine inserted.
  2. Two chrome-plated 12mm linear rail Shafts clamped to the Lower Frame.
  3. Two linear ball bearing Bushings on each Shaft.
  4. Springs that fit over the Shafts to absorb recoil of the Upper Bracket.
  5. An Upper Bracket, H-shaped, that screws into the Bushings.
  6. A Scope Rail on top of the Upper Bracket, to which I fixed a scope with up to 32x magnification.
  7. In the center of the Upper Bracket are two side Clamp Plates with a V channel cut along their length for gripping the scope rail of any gun to be tested.  One of the Clamp Plates rides on pins with springs, and is pushed by a Camming Lever to quickly clamp and release the guns.

The second version of the fixture added threads on top of the Upper Bracket for attaching up to 20 pounds of weight to dampen recoil, as well as a tray in the front that held up to 40 pounds of lead to keep it from lifting off the bench when shooting .308 rifles.

Leave a Reply

Your email address will not be published. Required fields are marked *