The Facts and Myths of Heat Induced Barrel Movement

For many years now there has been the belief that a rifle with a pressure point in the forend of the gun stock contacting the barrel would when fired for any length of time begin to loose its aimpoint because of the expansion of the barrel causing the muzzle to change it's vertical position.  With the development of the Accurizer it was necessary to determine if this was in fact true or an urban legend.  During the development of the product the results seen at the target did not seem to confirm the theory.  Because of this we set out to test the effects of heat on a totally free floated barrel and the also the effects on the same barrel with the it supported in the forend of the gun stock by the Accurizer.  For those of you who may be interested the manner in which the tests were conducted and the results that were obtained are listed below: 

 Two Lilja 24" stainless benchrest barrels were used in the tests. They are nearly identical except one is a 6BR and the other chambered for a .243 Winchester tight neck. The .243 was Cryo treated and the 6BR was not.  

The test was conducted by heating each of the barrels in the oven with an indoor/outdoor digital thermometer probe inserted half way down the barrel. They were then brought up to 130 degrees F. Prior to the heating they were measured at the muzzle, the point where they would later be contacted by the concave delrin block pressure point of the Accurizer, and finally at the rear of the barrel where the threads begin with a digital caliper and again after they were heated.  After being heated they were installed back into the action free floated and the gun stock was placed on a bench. A dial indicator was placed at the center of the barrel tip and the barrel was allowed to cool. The cooling was aided by the use of a fan and as the barrel cooled the temperature of the barrel and the vertical movement was recorded. They are as follows:

Barrel Diameter at Ambient  76 Degrees F.  

Barrel Diameter at 130 Degrees F.

Total diameter change from ambient to 130 Degrees less than .001"

Dial indicator was not zeroed but simply read and recorded  when it was centered at the tip of the barrel.  Thermometer sensor lead remained in the barrel during cooling.

Total upward vertical deflection of muzzle during cooling back to ambient  0.0010"

Same test with barrel supported with approximately 2# positive pressure above barrel weight near the forend of the stock by concave delrin block:

Total upward vertical deflection of muzzle during cooling back to ambient 0.0003"

.243 Win. Barrel

Barrel Diameter at Ambient (78 Degrees F)

               Barrel Diameter at 130 degrees F.

Total diameter change from ambient to 130 Degrees less than .001"

Total upward vertical deflection of muzzle during cooling back to ambient  0.0013"


Same test with barrel supported with approximately 2# positive pressure above barrel weight near the forend of the stock by concave delrin block:

Total upward vertical deflection of muzzle during cooling back to ambient 0.0005"

Copyrighted by Aftermarket Innovations Salem, Oregon 2000

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